The scene was straight out of a horror film. A pretty, young college student was being held in a headlock by a masked intruder with a loaded gun to her head, police said. Then, the gunman took aim at an officer. Within a moment, the officer pulled the trigger, leaving the Hofstra University student, Andrea Rebello, and the gunman, dead.

Michele Galietta, a professor of psychology at the John Jay College of Criminal Justice, who helps train police officers, spoke Sunday as Hofstra University students honored Rebello, the popular 21-year-old public relations major, by wearing white ribbons at their graduation ceremony.

"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 Galiento. "That's what makes the job of an officer amazingly difficult."

The mourning family of the student would disagree. Upon hearing that she died from a police bullet, the family was driven into more grief. 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.

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.

As far as police procedure goes, the Nassau County district attorney would determine whether an officer's use of deadly force was justified. A spokesman for the prosecutor's office said Monday it is monitoring the ongoing police investigation.

Rebello's funeral is scheduled for Wednesday in Sleepy Hollow, north of New York City.