BILLINGS, Mont. - Authorities are considering whether to bring criminal charges against a Montana 17-year-old who fired a bullet through his bedroom window and killed a friend, in a case an investigator has described as an accident.

The unidentified suspect had been startled when 15-year-old Mackeon Schulte and another friend knocked on his window early Sunday, Billings police said.

The alarmed teen grabbed a revolver, described as a family heirloom, and shot through the glass, striking Schulte in the head, police said.

Police are investigating the shooting as a homicide, and authorities are expected to weigh if negligence played a role in Schulte's death. It will be up to prosecutors to decide on charges. Billings Police Capt. John Bedford said the suspect was not considered an immediate danger, and criminal charges could run the risk of "compounding a horrible situation."

"We're not going to rush to judgment," he said. "There's enough damage that's already been done."

Prosecutors are planning a lengthy review, Yellowstone County Attorney Scott Twito said.

Montana law recognizes three types of homicide - deliberate, mitigated and negligent - and all three will likely be options for prosecutors, Andrew King-Ries, associate dean at the University of Montana School of Law, said.

Deliberate homicide, or murder, comes into a play when someone knowingly causes another person's death, King-Ries said.

Mitigated homicide is when a person kills someone while under some kind of mental or emotional distress.

Negligent homicide applies when a person should be aware that their actions could cause a death but chooses to disregard that risk.

"When you shoot a gun, you're probably aware there's a risk," King-Ries said. "If you can establish negligence, it's not an accident."

Bedford said charges of negligent homicide likely would be considered. "You don't necessarily have to have intent," he said. "Was this young man negligent in not identifying his target before firing the gun?"

Prosecutors have broad latitude on whether to file charges and can consider the wishes of the victim's family, who weren't available for comment Tuesday.

But "there's going to have to be some kind of acknowledgment of what this young man did," Bedford said.

Prosecutors also will have to consider whether a defendant can claim a killing was justified under Montana's "castle doctrine" of self-defense.

That strategy was used unsuccessfully last year when a Missoula homeowner shot and killed a German exchange student.

Attorneys for defendant Markus Kaarma asserted the shooting was justified under the castle doctrine because the student was trespassing in their client's garage. Jurors rejected the argument, and Kaarma was sentenced to 70 years in state prison on a charge of deliberate homicide.

Both the victim and the suspect in the most recent case went to Billings Senior High School, where several classmates described them as good friends.

Freshman Betty Mitchell said the two were close and that the suspect's house had been broken into previously. He was probably scared when he heard noises outside his window, she said.

Neighbors described the suspect as friendly.

"He's a great kid, and it's a really nice family," said Emily Duncan, who lives next door. "We're just sad they're going through this."