NEW YORK - The police officer who accidentally killed a Long Island college student along with an armed intruder faced perhaps the most harrowing decision in law enforcement: choosing the split-second moment when the risk is so high that you must pull the trigger.
That's the moment authorities say a Nassau County police officer experienced early Friday morning when a masked man holding 21-year-old Andrea Rebello in a headlock pointed a loaded handgun at him.
"The big question is, how do you know, when someone's pointing a gun at you, whether you should keep talking to them, or shoot?" said Michele Galietta, a professor of psychology at the John Jay College of Criminal Justice who helps train police officers. "That's what makes the job of an officer amazingly difficult."
She spoke Sunday as Hofstra University students honored Rebello, a popular public relations major, by wearing white ribbons at their graduation ceremony.
On Saturday evening, flags on the Hempstead campus were at half-staff and students held a silent outdoor vigil in front of a photo of the young woman. Surrounded by candles and flowers, they sang "Ave Maria."
Rebello's funeral is scheduled for Wednesday in Sleepy Hollow, in Westchester County, north of New York City.
Her life ended in the seconds that forced the veteran police officer to make a fatal decision, but the questions surrounding the student's death are just beginning, along with an internal investigation by the Nassau County Police Department.
The bare facts are simple. Rebello and the intruder, Dalton Smith, died early Friday when the officer fired eight shots, hitting him seven times, with one bullet striking Rebello once in the head, according to county homicide squad Lt. John Azzata.
With a gun pointed at her, Smith "kept saying, 'I'm going to kill her,' and then he pointed the gun at the police officer," according to Azzata.
The officer acted quickly, saying later that he believed his and Rebello's life were in danger, according to authorities.
No doubt, he was acting to try to save lives - his own and that of the young woman, Galietta said.
"What we're asking the cop to anticipate is, 'What is going on in the suspect's mind at the moment?'" she said. "We're always trying to de-escalate, to contain a situation, but the issue of safety comes in first, and that's the evaluation the officer has to make."
Eugene O'Donnell, a former New York City police officer and professor of law and police studies at John Jay College, said the crucial issue may be whether or not police had deemed it a hostage situation. If so, he said, there are protocols police follow to buy time, slow down, isolate and assess.
But O'Donnell said the officers may have had few options because of "an eyeball to eyeball confrontation between the officer and the offender."
"It may have been too fluid to deteriorate for the officers to do anything else," O'Donnell said. "It underscores that there's no two of these that are exactly alike."
Police tactical manuals are meant to assist officers in making the best decision possible, but in the end, "they're not 100 percent foolproof," Galietta said. "In a situation like that, you can follow procedure, and it doesn't mean it comes out perfectly."
The officer who fired the shots is an eight-year NYPD veteran and has been with Nassau County police for 12 years.
He is now out on sick leave, Azzata said.
Procedurally, the Nassau County district attorney's office would determine whether an officer's use of deadly force was justified. O'Donnell said. A spokesman for the district attorney's office did not respond to a request for comment Saturday night.
There are some rules governing the use of force for New York police officers. A subsection of Article 35 of New York Penal Law prohibits against recklessly endangering innocent people.