Sleepy Hollow High School via AP
Andrea Rebello, as seen in this image from from the 2010 Sleepy Hollow High School yearbook.
Patrol officers confronted with a hostage situation are taught to keep their distance if possible, set up a perimeter and wait for negotiators and SWAT teams to arrive.
That scenario has a high success rate: FBI data show that in the vast majority of these volatile cases, the victim is released or rescued unharmed.
Tragically, that's not how it unfolded early Friday on Long Island when, police say, a home-invasion robber holding a Hofstra University student at gunpoint came face-to-face with a cop who fired eight times, killing the suspect and his captive, 21-year-old Andrea Rebello.
The incident is still under investigation with many details unknown, but experts in police tactics say the chance for a peaceful resolution diminished the moment police crossed the threshold of the Uniondale, N.Y., home and set eyes on ex-con Dalton Smith.
Nassau County Police Department via AP
Dalton Smith, seen here in an undated police photo, was holding Andrea Rebello hostage when police confronted him and shot him and her dead.
"Once they're confronting a suspect with a gun, they have two options: back out and call SWAT or engage in negotiation or deadly force with the suspect," said Stuart Meyers of the police-training firm OpTac. "You can't really second-guess their decision."
A key question will be why they decided to go inside the house.
At a press conference over the weekend, Nassau County police said the two officers who first arrived on the scene had no idea a hostage was involved.
They were dispatched after one of the home's residents, sent out by the robber to get money from a cash machine, dialed 911.
When they arrived, Smith allegedly ordered Andrea's twin, Jessica, to answer the door and say everything was fine. Instead, she ran from the home, screaming, "He's got a gun."
When the officers entered they found Smith, along with Andrea and a male student. The male managed to get away, but the gunman kept the young woman in a headlock, training his gun on her as he tried to back out a rear door.
"When he realizes there is a police officer behind a wall in the hallway, he now moves her even closer to the front of his body," police Lt. John Azzata told reporters.
Then Smith pointed his gun at one of the officers, who fired eight rounds, Azzata said.
One shot hit Rebello in the head, killing her. Her godfather, Henry Santos, told the Associated Press the news she was struck down by a police bullet was a "second shock" for the grieving family.
David Klinger, a former officer and expert on police-involved shootings, said investigators will want to find out exactly what the officer who pulled the trigger knew before entering.
If he believed the only person inside was the gunman, there may have been no reason to go in without heavy backup, he said. If he suspected someone was being held at gunpoint, waiting for negotiators might have been more prudent.
But, Klinger noted, if he knew both the suspect and victims were in the house but was unsure of what was happening, going through the door could have been the right move.
"Let's say there's an armed robber in the house and a woman hiding in the closet ... if I can get in there and help this woman, then I do it," said Klinger, an associate professor of criminology at the University of Missouri-St. Louis.
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In this case, it's unclear if the 911 caller, the dispatcher, the officers themselves or a combination of all three added to the confusion.
Experts agreed that once the cops were inside and saw there was a hostage, their options were severely limited.
Despite the terrible outcome, the officer who fired — who has 20 years of law-enforcement experience — broke no laws in using deadly force and may not have violated police guidelines.
"When a gun is pointed at your face, second-guessing goes out the window," said Charles Key, former head of firearms training for the Baltimore Police Department and a consultant in police-involved shootings.
"Officers are trained to fire as many shots as necessary," Key said. "And you can fire eight rounds in less than two seconds."
Unlike tactical units who fire 50,000 practice rounds a year, a patrol officer usually has firearms training just twice a year, he said. In Uniondale, cops with the extra training were on their way but didn't get there before Rebello and Smith were dead.
The officer who shot Rebello is on sick leave. Law-enforcement trainers said it's impossible to predict if he will return to active duty. Even cops who kill criminals are sometimes too shaken to think about firing their gun again.
As police and prosecutors try to determine what missteps -- if any -- were made, no one will be trying harder to find answers than the cop who fired the eight shots, Key said
"This officer is going to second-guess himself until it eats him alive," he said.