east, to a story with new questions about police responding in a moment of crisis. As families gather for a joyful graduation at hofstra university, in their minds, the story of a young woman killed... See More
east, to a story with new questions about police responding in a moment of crisis. As families gather for a joyful graduation at hofstra university, in their minds, the story of a young woman killed in a hostage stand-off. N shot not by an intruder, but by police. Here's abc's gio benitez. Reporter: It was the moment of crisis that played out inside this house. He's got the gunpointed at head. Reporter: Inside, police say 21-year-old hofstra junior andrea robello was being held hostage by an ex-con -- dalton smith, who had released another hostage who called 911. Negotiators were dispatched, but a police officer got her first and made a critical decision, he went inside the house. Sources say that was officer nikolas budimlic, a decorated 12-year veteran of the force. He's with the originals and the gunman. Shots fired! Police say officer budimlic soon found himself face to face with smith, who was holding robello in a head lock, using her as a human shield. According to police, smith aimed his gun at the officer. The officer then raised his own weapon -- and fired. Seven bullets hit and killed smith, but one hit robello in the head -- killing her too. Today, questions. Should the officer have taken that shot? Police officers go through extensive training, but many departments use simulated videos like this. Officer gene o'donnell tells us, -- that it was a split-second decision. Ultimately the way it played out, it was probably one nano second which the officer had to make the decision. Reporter: The other big question, why did the officer go into the house? In a hostage situation, general protocol is to wait for negotiators. If you have credible information, you wait outside and you get specialized units, negotiators, and really you buy time. That's what you do, ideally, if you can. Reporter: Law enforcement across the country will be looking for lessons. Meanwhile, andrea robello was remembered at hofstra yesterday.
This transcript has been automatically generated and may not be 100% accurate.