In law enforcement, as in most every other profession, there are good ones and bad ones, but what most people seem to remember are the really bad ones.

Manuel Pardo, a former Florida police officer turned serial killer who was executed Tuesday, was one of the latter, officials say. He shot nine people to death in the late 1980s, claiming he was a ”soldier” ridding the streets of the wicked.

Most of Pardo's victims were reportedly involved with drugs, and Pardo claimed he was doing society a favor by ridding the streets of low-lifes who “have no right to live.” Authorities say he was a cold-blooded serial killer; one retired detective described him as “Ted Bundy-esque," while a retired prosecutor called him “very cold.”

Michael Tabman, a former Fairfax County, Va., police officer and former FBI agent, said law enforcement agencies have better screening tools these days to weed out potential problem applicants, "but we haven't perfected predicting behavior."

'Death Row Romeo' faces execution in Florida

He said people attracted to police work often have personalities that are "machismo-oriented" and "comfortable with a lot of authority," among other traits.

"A lot of that is a type of personality that in a perfect storm … can morph into anti-social behavior," said Tabman, an author who also blogs about crime and security. 

Herewith are some other notorious cases involving cops gone bad:

M. Spencer Green / AP file

Former Bolingbrook, Ill., police Sgt. Drew Peterson arrives at the Will County Courthouse in Joliet, Ill., for his arraignment on charges of first-degree murder on May 8, 2009.

Drew Peterson
The former Bolingbrook, Ill., police sergeant was convicted in September of murdering his third wife, Kathleen Savio, who was found dead in her bathtub in 2004. Authorities presume his fourth wife, Stacy Peterson, who vanished in 2007, is also dead; Peterson is a suspect but has never been charged in that case.

Before his 2009 arrest, according to media reports, Peterson seemed to taunt authorities, joking on talk shows and even suggesting a "Win a Date With Drew" contest.

After his conviction, Savio’s family members said justice was finally served. "Game over, Drew," Stacy Peterson's sister, Cassandra Cales, said. "He can wipe the smirk off his face. It's time to pay." 

Via KTLA / AP file

A frame from a video shot by George Holliday from his apartment in a suburb of Los Angeles shows a group of police officers beating Rodney King as other officers watch on March 31, 1991.

Rodney King beating
It was perhaps the most famous of all homemade videos – the 1991 clip of Los Angeles police officers beating black motorist Rodney King following a car chase.

A year later, a California jury acquitted three officers and deadlocked on charges for a fourth. The verdict sparked violent race riots in Los Angeles, and by the time order was restored, more than 50 people had died.

A federal jury later convicted two of the police officers, Stacey Koon and Laurence Powell, of a federal charge of violating King’s civil rights and sentenced them to 30 months in prison.

King died in June at age 47.

Katrina bridge shootings
In the chaos after Hurricane Katrina, six unarmed civilians were shot – two of them fatally – on the Danziger Bridge in New Orleans on Sept. 4, 2005. One of the dead, Ronald Madison, was a 40-year-old mentally disabled man who was shot in the back. Police claimed they opened fire because they thought people were shooting at them from the base of the bridge.

Getty Images file

Cars pass over the Danziger Bridge July 14, 2010 in New Orleans.

In August 2011, four former New Orleans police officers -- Kenneth Bowen, Robert Gisevius, Anthony Villavaso and Robert Faulcon – were convicted of civil-rights violations and firearms and other charges in the shootings. A fifth former officer, Arthur "Archie" Kaufman, who was assigned to investigate the shootings, was convicted of helping to orchestrate a cover-up.

“The officers who shot innocent people on the bridge and then went to great lengths to cover up their own crimes have finally been held accountable for their actions,” Thomas E. Perez, assistant attorney general for the Justice Department’s civil rights division, said when the men were sentenced to long prison terms in April.

Reuters file

Former New York City police officer Justin Volpe in 1997.

Abner Louima beating
Louima, a Haitian immigrant, was brutally beaten and sodomized with the handle of a toilet plunger in the bathroom of the 70th Precinct station house in Brooklyn, N.Y., after being arrested outside a night club in August 1997.

One cop, Justin Volpe, was sentenced in 1999 to 30 years in prison for what the judge called an “unusually heinous” crime and a “barbarous misuse of power.” Another, Charles Schwartz, who was initially accused of holding Louima down, pleaded guilty to perjury and was given a five-year sentence. Two other officers who were indicted for allegedly trying to cover up the assault had their convictions reversed due to insufficient evidence.

Chicago Sun-Times / AP

Former Chicago police officer Jon Burge, convicted of lying about the torture of suspects, walks to his attorneys' office following the first day of his sentencing hearing at the federal building in Chicago on Jan. 20, 2011.

Louima sued New York City and its main police union and won a $8.75 million settlement.

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Jon Burge
Burge was a former Chicago Police Department detective and commander who, along with the “Midnight Crew” of officers under his command, allegedly beat and tortured criminal suspects in the 1970s and '80s in order to gain confessions. Victims said they were burned with cigarette butts, smothered with plastic bags, shocked in the genitals and forced to play Russian roulette with a .44-caliber gun.

Although Burge was protected by the statute of limitations on the claims of abuse, he was convicted of lying about the torture. He was sentenced in January 2011 to 4 ½ years in prison.

The city agreed to pay more than $7 million to settle two torture lawsuits involving Burge.

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Joe Klamar / AFP - Getty Images file

Rodney King speaking with fans before presenting his autobiographical book 'The Riot Within...My Journey from Rebellion to Redemption' in Los Angeles.

Rodney King's death was ruled accidental in an autopsy report released Thursday by the San Bernardino County Coroner's Office, which also noted he had marijuana, cocaine and alcohol in his system.

The report summarized the events leading to his June 17 death at age 47 in his backyard pool in Rialto, Calif.

King "was in a state of drug and alcohol induced delirium," according to the coroner's report.

He "either fell or jumped into the swimming pool," the report said. "The effects of the drugs and alcohol, combined with the subject's heart condition, thus incapacitated, was unable to save himself and drowned."

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King's fiancée, Cynthia Kelley, found him in the deep end of the pool at 5:25 a.m. and called 911. She made several attempts to pull him out of the pool but was unable to save him. He was taken to Arrowhead Regional Medical Center where he died.

Rialto police said the preliminary investigation suggested the drowning was accidental and that there were no signs of trauma or foul play.

Kelley told police that King he had been out all weekend with a male friend, but police said at the time they did not know if King and his friend had been partying all night.

During a press conference announcing the death, police technicians could be seen bringing out a marijuana plant from inside King's home.

LA Riots 20 Years Later

King was an admitted drug addict and alcoholic and told NBCLosAngeles.com in April he had been managing his addictions.

King was remembered during services led by the Rev. Al Sharpton as a "symbol of forgiveness" who bore the scars of his infamous videotaped beating by Los Angeles police officers with dignity.

Sharpton said that King never showed bitterness to the officers who beat him.

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King became famous after his videotaped Lake View Terrace beating by Los Angeles police in 1991 was broadcast worldwide, as were photos of his bloodied and bruised face.

Those images became a national symbol of police brutality.

When four officers charged with felony assault on King were acquitted by a jury with no black members, the verdict sparked a riot that lasted for six days and brought U.S. military presence to patrol LA streets.

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During the unrest, which left more than 50 people dead and caused more than $1 billion in property damage, King famously pleaded for peace by asking, "Can we all get along?"

King's words were embroidered on the lid of his casket, next to a portrait of him.

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Joe Klamar / AFP - Getty Images file

Rodney King is seen on April 30 speaking with fans in Los Angeles before an event promoting his autobiographical book "The Riot Within...My Journey from Rebellion to Redemption."

Rodney King was remembered during a Saturday service at Forest Lawn in the Hollywood Hills as a "symbol of forgiveness" who bore the scars of his infamous beating with dignity.

The Rev. Al Sharpton, who delivered the eulogy, said at a news conference before the funeral that King never showed bitterness to the officers who beat him.

"People should not be judged by the mistakes that they make, but by how they rise above them," Sharpton said. "Rodney had risen above his mistakes, he never mocked anyone, not the police, not the justice system, not anyone."

Sharpton added that King had become a "symbol of forgiveness."

King was found in the bottom of his swimming pool in the backyard of his Rialto home on June 17. His death at age 47 is being treated as an accidental drowning, though autopsy results have still not been released.

Family members held a private service early Saturday, followed by a public memorial and burial.

"I will remember his smile, his unconditional love," said daughter Laura Dene King, 28, to a phalanx of news cameras outside the Hall of Freedom at Forest Lawn-Hollywood Hills. "He was a great father, a great friend; he loved everyone. People will just have to smile when they think of him."

Donors who had contributed to the funeral and other arrangements included TV producer Anthony Zuiker, who donated $10,000.

"We lost a symbol, but they lost a loved one," said Zuiker, creator of the CSI: series. "Rodney was a healer."

King became famous after his videotaped Lake View Terrace beating by Los Angeles police in 1991 was broadcast worldwide, as were photos of his bloodied and bruised face.

Those images became a national symbol of police brutality.

"That showed what was evident all over the United States, that police brutality was alive and well," observed Lawrence Tolliver, the owner of well-known barber shop in South LA.

When four officers charged with felony assault on King were acquitted by a jury with no black members, the verdict sparked a riot that lasted for six days and brought U.S. military presence to patrol LA streets.

During the unrest, which left more than 50 people dead and caused more than $1 billion in property damage, King famously pleaded for peace by asking, "Can we all get along?"

King's words were embroidered on the lid of his casket, next to a portrait of him.

Grant Hindsley / AP

The Rev. Al Sharpton, right, speaks to reporters before the public memorial service for Rodney King at Forest Lawn-Hollywood Hills in Los Angeles on Saturday.

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Updated at 3:34 p.m. ET: Rodney King, the black motorist whose videotaped beating by Los Angeles police officers in 1991 sparked some of the deadliest race riots in U.S. history, was found dead Sunday, police said. He was 47.

Police in Rialto, Calif., found King's body in a swimming pool after getting a 911 call from his fiancee, Rialto Police Capt. Randy DeAnda told NBC News. Officers pulled King from the pool and began doing CPR, but he was unresponsive.

King was transported to Arrowhead Hospital in Colton, where he was pronounced dead at 6:11 a.m. PDT, DeAnda said.

The San Bernardino County coroner will perform an autopsy.

"Right now we have no reason to believe there was foul play because of the circumstances," Rialto Police Sgt. Richard Royce told msnbc.com. "The evidence is that it was a simple drowning."

Rodney King: 20 years after L.A. riots, 'Can we all get along?'

Homicide detectives continued to investigate mid-Sunday morning, Royce said, although he called the investigation "a standard death investigation."

Kevork Djansezian / Getty Images

Detective Carla McCullough, right, of Rialto police directs a police photographer as they investigate the death of Rodney King, who was found in his pool on Sunday.

A file photo from the Los Angeles Times shows that the pool is oval and that King had erected tarps around it to prevent neighbors from peering in. Two dates are inscribed along the pool wall: 3/3/91, the day King was beaten, and 4/29/92, the day a jury acquitted three of the four officers who beat him.

King was beaten by Los Angeles Police Department officers on a dark street on March 3, 1991, after he was stopped for speeding. Four officers hit him more than 50 times, kicked him and shot him with stun guns. A bystander videotaped much of the incident from a distance.

A year later, a California jury acquitted three of the four officers, three of whom were white and one Hispanic. The jury deadlocked on one of the charges for Officer Laurence Powell.

The riots that erupted on April 29, 1992, were among the most lethal in U.S. history. By the time order was restored, more than 50 people had died, nearly 3,000 were injured and thousands of businesses were damaged or destroyed.

In one of the most searing images from the riots, a 33-year-old white construction worker named Reginald Denny was pulled from his vehicle and beaten unconscious by four men at a Los Angeles intersection. Twenty years later, he has still not recovered from his injuries.

The violent reaction prompted King's famous plea on television: "Can we all get along?"

Gene Blevins / Reuters

A former bodyguard for Rodney King, Johnnie Kelly, left, walks with one of King's daughters Dene King, center, outside her father's home in Rialto, a suburb of east Los Angeles, on Sunday.

Nearly a year later, a federal jury convicted two of the police officers of a federal charge of violating King’s civil rights and sentenced them to 30 months in prison. Two other officers were acquitted. King eventually received a $3.8 million settlement from the city, and the case led to sweeping changes in the LAPD.

The police chief, Daryl Gates, came under intense criticism from city officials who said officers were slow to respond to the riots. He was forced to retire. Gates died of cancer in 2010.

20 years later: Have race relations improved?

In the two decades after he became the central figure in the riots, King was arrested several times, mostly for alcohol-related crimes. He later became a record company executive and a reality TV star, appearing on shows such as "Celebrity Rehab."

In an interview earlier this year with The Associated Press, King said he was a happy man.

"America's been good to me after I paid the price and stayed alive through it all," he said. "This part of my life is the easy part now."

King had recently been promoting his just-published memoir, "The Riot Within: My Journey From Rebellion to Redemption." The book came out around the 20th anniversary of the L.A. riots.

King, who has three children, was engaged to marry Cynthia Kelley, a juror in the civil suit he brought against the city of Los Angeles, according to the biography that accompanied his book.

The Los Angeles Times published a quote that King gave the newspaper earlier this year: "I would change a few things, but not that much. Yes, I would go through that night, yes I would. I said once that I wouldn't, but that's not true. It changed things. It made the world a better place.''

Slideshow: Los Angeles riots: 20 years later

Hyungwon Kang / Reuters

Revisiting a turbulent chapter in race relations

Launch slideshow

Reuters and The Associated Press contributed to this report.

Twenty years ago this weekend, riots broke out in Los Angeles – and spread to other cities – after a California jury acquitted three white and one Hispanic Los Angeles police officers in the videotaped beating of black motorist Rodney King.

The riots that erupted on April 29, 1992, were among the most lethal in U.S. history. By the time order was restored, 53 people had died, nearly 3,000 people were injured and thousands of businesses were damaged or destroyed.

In one of the most searing images beamed into living rooms across the country from the disturbance, a mostly black mob enraged by the acquittal dragged white truck driver Reginald Denny from his cab at a south Los Angeles intersection and beat him unconscious while news helicopters hovered overhead.

Nearly a year later, a federal jury convicted two of the police officers of a federal charge of violating King’s civil rights and sentenced them to 30 months in prison. Two other officers were acquitted. King eventually received a $3.8 million settlement from the city, and the case led to sweeping changes in LAPD.

More recently, King has been promoting his just-published memoir, "The Riot Within: My Journey From Rebellion to Redemption."

AP Photo/George Holliday/Courtesy of KTLA Los Angeles

The beating of Rodney King by a group of Los Angeles police officers was captured on videotape by a citizen.

As Los Angeles, and the nation, reflects on the anniversary this weekend, many are asking the same plaintive question King uttered on the steps of city hall during the riots two decades ago: "Can we all get along?"

Many seem to agree that the city is safer today and relations between ethnic groups have improved. A recent poll of Los Angeles residents by the Center for the Study of Los Angeles at Loyola Marymount University found that most say L.A. is unlikely to see a repeat of such riots in the coming years.

NBCLosAngeles.com has a special package of stories and videos about the 20th anniversary of the riots here.

Do you think race relations have improved? Take the poll below and then join the discussion on Facebook.

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