Daniel Holmes for NBC News

Brittany Loring, right, and Liza Cherney, both of whom were seriously injured in the Boston Marathon bombings, lead the procession Monday at the Carroll School of Management commencement ceremony at Boston College in Chestnut Hill, Mass.

Before she was seriously wounded in the Boston Marathon bombings, Brittany Loring didn’t have to give much thought to her graduation walk.

But on Monday, after ditching the single crutch she had been using during her recovery, she walked with a stiff limp to collect her diploma from Boston College’s Carroll School of Management -- passing a “milestone,” she said, as she recovers from the horrible events of April 15. She was joined by a close friend, Liza Cherney, who was also hurt and was graduating from the program.

“This is the first step to overcoming it," Loring told NBC News before the ceremony. "It’s definitely showing that the individuals that committed this crime are not holding me back. At least in terms of the goals that I had prior to the event and post event, they haven’t changed.” 

Loring, who earned an MBA degree on Monday, was cheering on friends in the city’s iconic road race as part of her 29^th birthday celebration when the bombs exploded. She suffered a skull fracture and concussion, was struck by BB pellets -- including one in the neck and two in the head, and had wounds on both of her upper thighs, likely from shrapnel.

After three surgeries to clean and close the wounds, and weeks of occupational and physical therapy, Loring managed to walk for the first time without crutches last week, lasting as long as 15 minutes. She also has begun to venture into crowds again, a daunting prospect for some of the injured, and resumed some of her routines, such as visiting a local café. 

“I feel better every day," she said, noting she can now bend her knee to 90 degrees. "I seem to be moving pretty quickly in comparison to where I started.”

Loring’s classmates at Boston College, where she will also receive her law degree on Friday, sprung to action in the aftermath, making sure she wasn’t alone and was getting the care she needed. Cards, meals and flowers also streamed in.

“I knew that I had a tight group of friends … but I mean there is nothing like an event like this to really give people the opportunity to show how much they care,” she said. “After this event I just, I feel a lot closer to them … and I can see how much they respect and care for each other and for me.” 

Boston College said it waived Loring’s final exams and last assignments so she could graduate with her class.

On Monday, Loring walked alongside Cherney, who said she was struck by a lot of shrapnel in one leg. The friends bore big smiles under sunny Boston skies. 

Daniel Holmes for NBC News

Brittany Loring receives her diploma Monday.

“I expect that we will be friends forever," Loring said. "We’re really close and I’m so happy that she’s doing as well as she is and that we will be able to move forward and carry on.” The shared walk in the ceremony “definitely has a lot of meaning for me,” she added.

Though it was such an accomplishment to achieve the MBA, Cherney said the day took on greater significance after the attacks.

"It is more special because I feel very close to so many people who are graduating with us today, even closer than before,” she told reporters after the ceremony.

The pair was among 275 injured in the attacks. Loring will join some of the injured at a local rehabilitation hospital later this week, where she will do outpatient therapy. Eighteen people remain hospitalized after the bombings as of Friday.

"I’ve been trying to get things back to normal and that’s not always easy," Cherney said. "Just seeing that you can’t do things that you used to be able to do as easily has been a struggle. And also, I mean, from an emotional standpoint every once in a while it’s tough, but I think that ... you’ve got to push through.”

Doctors haven’t given Loring a time frame for a full recovery, but she plans to walk in her wedding in September and to start her job in international tax in October.

Reflecting on the attacks, she said she has had her ups and downs emotionally.

"It is life changing in some ways," she said. " ... but I hope that it will only be in a positive way, and that it will just make me a better person for it.  ... I hope that I will be able to do good in my life because of this understanding.”

To donate to Brittany Loring, her family has set up this fund. And for Liza Cherney, this fund.

NBC freelance photographer Daniel Holmes contributed to this report.

Related:

Marathon bombing victims adjust to a 'different normal'

Full coverage of the Boston Marathon tragedy on NBCNews.com

Vkontakt

From left: Azamat Tazhayakov, Dias Kadyrbayev, and Dzhokhar Tsarnaev. A photograph from Dzhokhar Tsarnaev's page on VKontakt, the Russian equivalent of Facebook, appears to show him in Times Square. It is believed to be from November 2012. New York Police Commissioner Ray Kelly said authorities knew of two trips by Dzhokhar Tsarnaev to New York in 2012 but said he did not know whether those visits were related to any plot against Times Square.

Two of the three people newly arrested in the Boston Marathon investigation are Kazakh friends of Dzhokhar Tsarnaev, and one drove a BMW with a novelty license plate that said “Terrorista #1,” according to people who knew them.

The two were pictured in a 2012 photo with Tsarnaev in Times Square that was posted to VKontakt, the Russian equivalent of Facebook. Authorities say Tsarnaev and his brother, suspected in the marathon attack, discussed driving to New York and setting off more of their explosives there.

The Kazakh men, Azamat Tazhayakov and Dias Kadyrbayev, were charged Wednesday with conspiring to destroy or hide a laptop belonging to Tsarnaev and a backpack of his containing fireworks.

Another man, Robel Phillipos of Cambridge, Mass., was charged with lying to investigators. All three appeared in federal court in Boston Wednesday afternoon.

Both Kazakh men are 19 and were in the United States on student visas, the Justice Department said.

Stephen Troio, who said he lived on the same dorm floor as the two men during his freshman year in 2011, said that they showed “lack of emotion” and “lack of personality” and that nothing stood out about them but the BMW.

“They did have a lot of money,” Troio told NBC News. “He wrecked like three Beamers and then bought another one.”

Trevor Berry, 20, who took a calculus course with Tazhayakov, said the Kazakh was friendly with Tsarnaev and that the two could be spotted dining together on campus. “They were pretty close as far as I can tell,” he said.

Berry said that Tazhayakov was "much more quiet than Dzhokhar," but was once "really flustered" over a low grade he'd gotten in calculus class.

The two men were taken into custody over immigration violations last week. Kadyrbayev’s lawyer, Robert Stahl, told The Associated Press then that they were horrified by the marathon bombing.

“They can’t even fathom something like this from a kid who seemed to be a typical young college student,” he said.

The two Kazakhs lived at an apartment in New Bedford, Mass., near the campus of the University of Massachusetts’ Dartmouth campus, where Tsarnaev was a student. Last week, investigators scoured a landfill in New Bedford for items that might belong to Tsarnaev, including the laptop and receipts related to the purchase of fireworks.

A neighbor in New Bedford said Wednesday that the Kazakhs were quiet and polite, and would even help carrying groceries inside. They had parties, the neighbor said, including one that police were called to at 3 a.m.

Stahl told the AP that the two men did not see Tsarnaev in the days before or after the marathon attack.

The license plate was a joke gift from friends of Kadyrbayev’s friends, meant to refer to his late-night partying and not his political sentiments, Stahl told the AP. The license plate was pictured in Tsarnaev’s Twitter feed in March.

A Facebook page in the name of Azamat Tazhayakov lists him as a UMass-Dartmouth student and as a member of the Class of 2011 at a Kazakh school, Miras International School Astana. It lists his hometown as Atyrau, says he speaks Russian and lists Rihanna, Beyonce and Enimem as musicians he likes.

A Facebook page in the name of Dias Kadyrbayev shows him vacationing in Fort Lauderdale, Fla., and palling around with friends.

This story was originally published on Wed May 1, 2013 3:12 PM EDT

The chairman of the House Homeland Security Committee said Sunday that federal authorities are investigating whether the suspects in the Boston marathon bombing received training that helped them carry out the deadly attack.

Rep. Michael McCaul (R-Texas) said during an appearance on Fox News Sunday that it was too soon to dismiss a possible connection between the suspects and foreign terrorists.

"Right out-of-the-box, U.S. officials unanimously are saying there's not foreign connection to this case when in fact the FBI just began its investigation into the case," McCaul said on Fox News Sunday. "They just got the computer. They just sent a U.S. team over to (the) Chechen region, and to Dagestan, to interview witnesses."

He added: "I think given the level of sophistication of this device, the fact that the pressure cooker is a signature device, goes back to Pakistan or Afghanistan, leads to believe — and the way they handled these devices and the trade craft leads me to believe that there was a trainer. And the question is, where is that trainer or trainers? Are they overseas in the Chechen region or are they in the United States?"

Publicly, U.S. officials investigating the bombing said there is no evidence of a wider plot, including training, direction or funding for the attacks.

And on CBS' Sunday morning show, Face the Nation, Sen. Claire MCaskill (D-Missouri) said there was no evidence the suspects were "part of a larger organization."

Dzhokhar Tsarnaev, 19, is charged with joining his older brother, Tamerlan, who's now dead, in setting off the bombs near the marathon finish line. The attacks killed three and wounded 264. The brothers are ethnic Chechens who came to the United States about a decade ago with their parents. Both parents now live in Russia.

McCaul said Sunday that the suspects' mother had contributed to their "radicalization" and would be detained for questioning if she returned to the United States.

Meanwhile, Reuters reported Sunday that the parents of the bombing suspects had scrapped plans to the travel to the United States.

During an interview from an undisclosed location in Russian, the suspects' father, Anzor Tsarnaev, told the wire service that he believed he would not be allowed to see his surviving son Dzohkhar, who was captured and has been charged in connection with the April 15 bomb blasts that killed three people and wounded 264.

"I am not going back to the United States. For now I am here. I am ill," Tsarnaev said. "Unfortunately I can't help my child in any way. I am in touch with Dzhokhar's and my own lawyers. They told me they would let me know (what to do)," he said.

Tsarnaev had said Thursday that he planned to travel to the United States to see Dzkhokhar and bury his elder son, Tamerlan, who was shot dead by police in a firefight four days after the bombings.

Reuters said Tsarnaev agreed to the face-to-face interview on condition that the village's location not be disclosed.

A young college police officer beloved by his colleagues has been identified by authorities as the latest casualty of the Boston Marathon bombing suspects.

Sean Collier, 27, of Somerville, Mass., was an officer at the Massachusetts Institute of Technology. He was found shot in his vehicle on the campus late Thursday night as authorities pursued two brothers named as suspects in Monday's deadly marathon attack.

In a statement his family said they were "heartbroken."

"Our only solace is that Sean died bravely doing what he committed his life to — serving and protecting others," the statement read. "We are thankful for the outpouring of support and condolences offered by so many people. We are grieving his loss and ask that the media respect our privacy at this time."

MIT Police Chief John DiFava described Collier as "a dedicated officer who was extremely well liked by his colleagues and the MIT community" in a press release on Friday.

“Sean was one of these guys who really looked at police work as a calling,” DiFava said. “He was born to be a police officer.”

Collier sustained multiple gunshot wounds, according to the Middlesex District Attorney in Massachusetts. He was transported to Massachusetts General Hospital, where he was pronounced dead.

Collier crossed paths with the two suspects, Dzhokhar and Tamerlan Tsarnaev, at approximately 10:20 p.m. Thursday night, authorities said — roughly five hours after the FBI released surveillance photos of the two men they say planted twin bombs near the finish line of Monday's Boston Marathon, killing three people and wounding 176.

The suspects shot Collier on the MIT campus in Cambridge, Mass., following an altercation, according to authorities. They then allegedly carjacked a Mercedes SUV, holding the driver hostage for a half hour before freeing him at a gas station in Cambridge, according to sources.

On their way to the neighboring town of Watertown, they tossed explosive devices outside the SUV’s window, officials said. In a long exchange of gunfire between the suspects and authorities, a transit officer, Richard Donahue, was seriously injured.

The older brother, Tamerlan, died after the gun battle early Friday morning. The younger sibling, Dzhokhar, was captured at about 8:45 p.m. Friday following a large manhunt.

In a tragic coincidence, Collier and Donahue were "actually really good friends” who graduated from the same 26-member police academy class together three years ago, according to Milton, Mass., police officer Michael Delaney, who went to the academy with them.

"It's bizarre," Delaney said. "To take two of them out of there, it's a decent percentage." 

Delaney, 36, said both Collier and Donahue lived in Somerville. He remembered Collier as a "technology nerd."

"He was definitely the smartest kid in the class. He built us a website that the instructors didn't know about, but we used as a forum to communicate with each other outside of class." Delaney said. "Sometimes [the teachers] weren't so clear on the instructions. It helped ensure that no one screwed up."

Delaney said he heard on the news last night that an MIT officer had been shot, and he immediately texted Collier. When his friend didn't text back, he started to worry. Hours later, he found out from a Facebook group he and other police officers from the academy are in that Collier was shot. 

"I don't even think his family knew at that point," he said. "He was a really nice kid.” 

Collier, who wasn't married, had only been a patrol officer at MIT since Jan. 9, 2012, according to the university. He was part of the MIT Outing club, which went on ski and hiking trips.

Noel Morales, a senior at MIT, said Collier was a regular presence at student events, eager to get to know the students he was protecting, according to MIT's press release.

“He was always really fun to hang out with,” Morales said.

Mechanical engineering student Matthew Gilbertson, who knew Collier from the Outing Club, said he and Collier were in a car accident a few months ago while driving to the White Mountains in New Hampshire.

“Sean was the first out of our car to go check and see if the [other driver] was OK,” said Andrew Ding, according to MIT's press release. “It would be exceedingly difficult to imagine him not stepping up and doing the right thing when he had the chance, which unfortunately he did last night.”

Somerville Alderman Bob Trane said he had been bombarded with phone calls from people wanted to express their condolences about Collier. 

Miranda Leitsinger / NBC News

From left: Gary Grandonico, Max Jaffe, and Tomas Isman, all 22 and students at Tufts University, lived a few doors down from Collier but didn't know him. Asked why they were had hung a flag, Jaffe said: "In solidarity. We didn't really know the police officer who got killed this morning, but we wanted to show our support."

"We are all feeling the loss," Trane said from a block away from where Collier lived. "He was wise beyond his years. I was just impressed by how he was so mature for his age." 

Before working for MIT, Collier was an IT civilian employee at the Somerville police department.

MIT's president said his death reverberated throughout the entire university community. 

“The loss of Officer Collier is deeply painful to the entire MIT community,” L. Rafael Reif said, adding that it was "senseless and tragic."

The school's executive vice president and treasure, Israel Ruiz, said, “The MIT Police serve all of us at the Institute with great dignity, honor and dedication. Everyone here — those who knew Officer Collier, and those who did not — are devastated by the events that transpired on our campus last night. We will never forget the seriousness with which he took his role protecting MIT and those of us who consider it home.” 

Authorities cordoned off Collier's home with yellow tape on Friday morning.

Collier's family asked for donations to be made in his name to The Jimmy Fund, which supports the Dana-Farber Cancer Institute in Boston. 

Related content:  

• Boston on lockdown during marathon manhunt 
• Profile of suspects in Boston Marathon bombing
• Photos from Bostonians locked down amid terror hunt 
• Timeline of terror hunt: From photo release to rolling shootout
• Slideshow: Bombings at Boston Marathon
• Tweeting police chatter creates confusion over Boston suspect

This story was originally published on Fri Apr 19, 2013 11:25 PM EDT

AP

This combo of photos released by the FBI Friday April 19 shows what the FBI is calling suspects number 1, left, and suspect number 2, right, walking through the crowd in Boston on Monday, April 15, 2013, before the explosions at the Boston Marathon.

As authorities closed in on the Boston Marathon bombing suspects -- one of whom was killed during a violent shootout in Boston's Watertown suburb early Friday -- Twitter and other social media outlets lit up with outtakes from police scanner reports, including a moment when eavesdropping tweeters heard the name of a missing Brown University student come over the airwaves in conjunction with the Monday attacks.

"Police on scanner identify the names of #BostonMarathon suspects in gunfight, Suspect 1: Mike Mulugeta. Suspect 2: Sunil Tripathi," read the most retweeted of the tweets, from the hacker group Anonymous. The post was retweeted nearly 3200 times.

But on Friday morning, it was certain: Tripathi was not involved with the bombings at all. Neither was the other named referenced. Authorities had identified the suspects as brothers with the last name Tsarnaev. Dzhokar, 19, was still wanted; his 26-year-old brother, Tamerlan, was dead after a night of violence that included the shooting to death of a Massachusetts Institute of Technology police officer, robbing a 7-Eleven, car-jacking a Mercedes SUV and injuring a Boston transit police officer.

In the age of live streaming audio and fast tweets, amateur sleuths can spread police scanner chatter -- which is just that, chatter -- more quickly than ever. But the dissemination of information comes with a risk: endangering law enforcement or the public.

"The last thing we want to become are reporters for the fugitive,"  Clint Van Zandt, former FBI profiler and NBC criminal analyst, said. "That's what I think people who tweet and post have to be careful of in the extreme and worst-case scenario. Are they giving information that would give aid and comfort to a killer? If you ask yourself that question and the answer is no, then go ahead and post it." 

Boston police mentioned Tripathi and the other less-known name on their scanner just before 1 a.m. Friday morning, about two hours after law enforcement officials first encountered the suspects they had been hunting since Monday's attack.

Missing student's family 'staggered' by false accusation

AP

This undated photo released by Brown University shows Brown University student Sunil Tripathi, who was last seen in the Brown campus area on Saturday morning, March 16, 2013 in Providence, R.I. For a few hours, social media lit up with reports that Tripathi was mistakenly identified as one of the Boston Marathon suspects.

Prior to the bombings, Tripathi's disappearance was reported to be a possible suicide. It's unclear why his name and Mulugeta's came up on the police scanner, but some on Twitter posted side-by-side photos of Tripathi and one of the Boston marathon suspects who had been seen on surveillance wearing a white hat. 

"Is there any doubt that Suspect #2 on the run is Sunil Tripathi?" wrote one, @HonestyInGov, comparing Tripathi's dark curly hair and thin frame to that of the suspect's.

Misinformation is not the only danger. As of Friday morning, nearly 83,000 were simultaneously streaming a live audio of Boston's police scanner from a single website, broadcastify.com. Listening to unfiltered feeds of Boston's police, fire, and emergency personnel comes with a responsibility for those people, says Van Zandt, the former FBI profiler.

Because the Boston suspects are believed to have been in the U.S. since 2002 or 2003, "they may well be subscribing to these blogs and tweets, and that gives them inside information," he said.

He added, though, that even broadcasting a live raid on television or cable can give away information to suspects, who could be watching their own search play out live.

"I've seen situations where the bad guys sit inside of a house or building, see which way the cops are coming, then start shooting from inside the door," he said. "Every time I talk on TV, I think the bad guy is listening. I think, what do I want him to hear? I keep trying to get a guy to surrender."

Related content:

'Dedicated officer' gunned down by Boston Marathon suspects at MIT

Profile of suspects in Boston Marathon bombing

Nearly 1 million told to stay indoors, transit canceled

Massive manhunt for 2^nd suspect after 1^st one killed 

Photos from Bostonians locked down amid terror hunt 

An amateur photographer who works in a downtown Boston office captured grim photos of the moment when the bombs went off as the marathon was finishing on Monday.

"I went to the window and I was looking in the direction of the finish line. I saw simultaneously a runner go down, a huge explosion, and then a deafening roar," Benjamin Thorndike said. "I had my camera in my hand, and I just pushed the rapid-shutter button down and just took 25 pictures over the course of what felt like a long time, but I think it was only 15 or 20 seconds."

None of the people in Thorndike's photos have been identified.

Courtesy Ben Thorndike

Courtesy Ben Thorndike

Courtesy Ben Thorndike

Courtesy Ben Thorndike

Courtesy Ben Thorndike

Courtesy Ben Thorndike

Courtesy Ben Thorndike

Courtesy Ben Thorndike

Hear Thorndike describe the experience in his own words, and watch the pictures in a video sequence, here.

Related content:

• As Boston bombing photos and videos pour in, where do investigators begin?
• Slideshow: Aftermath and reaction following Boston bombings
• Anatomy of a bombing: Photos show battery, wires used in device

Slideshow: Aftermath and reaction following Boston bombings

David Friedman / NBC News

Heightened security, empty streets, and memorials mark the the day after the Boston Marathon bombings.

Launch slideshow

The Boston marathon bombings that killed three and injured more than 170 people have shocked the nation and left Americans and the world grieving for the families of those who were killed and wounded.

Were you, a family member, or a friend among those hurt in the attack? Share your first-person account with NBC News, if you are well enough to do so. Tell us your age, where you're from, you're phone number, and your story. Select accounts will be published on NBCNews.com; we won't publish your phone number.

Email us here to tell your story.

LONDON -- British authorities ordered more police on the streets for Sunday's London Marathon in the wake of the Boston bombings, but experts warned it was "virtually impossible" to guarantee the safety of the hundreds of thousands who will attend the event. 

A police source said additional patrols by uniformed officers were planned to reassure the public in the wake of deadly attack.

While British security officials have been in contact with their counterparts in the U.S. following Monday's blasts, the U.K.'s threat level for international terrorism hasn't been changed from "substantial" -- the third of five categories on the scale.

At least 500,000 spectators are expected to watch Sunday’s race and Prince Harry is due to hand medals to the winners.

The course takes the 36,000 runners right past major sites - including Tower Bridge, the Houses of Parliament and Buckingham Palace – as well as through Canary Wharf, the giant riverside financial district targeted twice by the Irish militants in the 1990s.

Even in a city that has spent recent decades under the threat of bombs – first from Irish Republicans, more recently jihadists – such a public event poses a security headache.

Sir Bernard Hogan-Howe, the commissioner of London's Metropolitan Police, said that the force was "taking more more precautions than we might have done otherwise."

"We will make sure we've got more officers on the street looking after people, making sure they're kept safe, but we've no reason to think they'd be any less safe than before the terrible events in Boston,." he said. "We'd be professionally irresponsible if we didn't take some reasonable steps."

Sang Tan / AP

Backdropped by Buckingham Palace, a jogger crosses the Mall in London on Tuesday. It will be transformed into the finishing area for Sunday's London Marathon.

Metropolitan Police Commander Christine Jones declined to give details of what changes might be made, if any, to the event's security plan. She said officers would “continue to review all the intelligence” available.

London Marathon chief executive Nick Bitel insisted the event would go ahead. “We will be reviewing our security in the coming days, in the light of what has happened in Boston," Bitel told ITV News.

"I don't want to talk about specifics of what security we have had in the past, or will have on Sunday. All I can say is that it will be of an appropriate level to meet whatever threat assessment is made, in conjunction with the police," he added.

Hugh Robertson, a British government minister, called for crowds and runners to attend in London as normal.

“The very best way to show solidarity with Boston is to get out there on the streets of London to cheer the runners on and to show that we won’t be defeated by this sort of activity,” he told the London Evening Standard newspaper.

Runners will be encouraged to wear a black ribbon at the start of the race to honor victims of the Boston bombing, and a 30-second silence will be observed, organizers said Wednesday. 

NBC News national security analyst Michael Leiter said it was “virtually impossible” to make a marathon completely secure because of its 26.2-mile long route.

“You just have to do the best you can to keep people safe and maintain resilience," he said. “It’s important we don’t alter our lives because that provides the terrorist – domestic, international, whoever it may be – with a huge victory.”

Helmut Spahn, executive director of the International Centre for Sport Security, told Reuters: "There has to be a clear analysis of the situation and certainly no over-reaction. More police, more military is not always the best solution. To have a 100 percent security is very, very difficult if not near impossible.”

Sang Tan / AP

A sign warns of road closures linked to the forthcoming London Marathon.

This story was originally published on Wed Apr 17, 2013 2:29 AM EDT

LONDON -- Former Boston Police Commissioner Bill Bratton said Tuesday that those responsible for the bombing of the city’s marathon should be put to death.

Bratton said he had “every confidence” that the authorities would “get to the bottom of this and bring those responsible to justice.”

Massachusetts abolished capital punishment in 1984, but Bratton said the federal authorities could take over the prosecution of terrorist acts like this and a federal court could pass the death sentence.

“I think this act would be an appropriate use of the death penalty as a penalty for the crime,” he said.

Bratton, who was born and raised in the city and policed its marathon for many years, said he was having dinner in the British capital when he started getting emails about the bomb blasts.

He spent the next few hours trying to find out what happened and whether people close to him had been hurt or killed.

“I’ve friends and relatives that would be at that event, some running in it, some observing,” Bratton said, adding that former police colleagues would also have been there providing security.

'No shortage of haters'
Bratton, who was also previously chief of the Los Angeles Police Department and New York's police commissioner, said there were a number of potential suspects, including al Qaeda.

“You line up the usual suspects and they’d certainly be at the front of the line, but unfortunately there’s no shortage of haters, people who don’t like the government … neo-Nazi types … any number of people are capable of wanting to participate and pull of this type of event,” he said.

But Bratton cautioned against anyone jumping to conclusions or indulging in “idle speculation” about who had carried out the attack and said people should allow law enforcement officers to deal with the investigation.

He said the authorities had been successful in preventing many terrorist attacks in the U.S., including "at least a dozen" in New York City, where he now lives.

Slideshow: Boston Marathon explosions

Charles Krupa / AP

See images from the scene of the explosions.

Launch slideshow

Bratton said this was partly down to good intelligence and "citizen observation." "If something looks suspicious, if you see something, report it," he said.

He admitted it was not possible to prevent every attack, but urged people to carry on with normal life despite the terrorist threat.

“You don’t let them create such a fear that you change the way you live,” he said. “We will move on. We will remember, we’ll commemorate, we’ll mourn, but life goes on."

However, speaking earlier on MSNBC's "Morning Joe," Bratton said the bombing would have a lasting effect. 

“I grew up in Boston. It [Patriots’ Day and the marathon] is an extraordinary day and one that I have great memories of," he said. "And those memories will be forever tainted.”

Related:

Full coverage of the Boston Marathon bombings from NBC News

Boston on high alert after marathon bombing kills 3, injures scores

Boston Marathon victims include two brothers who each lost a leg