Story highlights A schizophrenic teen calls for help subduing him; a detective shoots him

Lawyer: The detective fired because he feared another officer's life was in danger

The late teen's family says the detective's actions are unconscionable

Experts: Police should fire if there is an 'objectively reasonable' threat

A man calls 911 saying his family needs help. His wife is scared of their schizophrenic son, armed with a screwdriver. One, then two, then three law enforcement officers -- all from different agencies -- arrive. After the situation calms somewhat, according to the family, a tussle ensues.

What happens next?

In a case this week out of Boiling Spring Lakes, North Carolina, one officer responded by firing his gun, killing 18-year-old Keith Vidal , who was mentally ill.

The teen's furious family soon take their case public, saying there's no justification for Sunday's shooting. Vidal, they say, weighed all of 100 pounds; he was mentally ill, yes, but he was a "good kid."

CNN first learned of the shooting through an iReport sent by a family friend

Veteran defense attorney Mark O'Mara, a CNN legal analyst, agrees with the family. From what he knows of the case -- including the police detective first saying he was 'defending himself," only to later say through his lawyer he was defending another officer -- O'Mara thinks "deadly force was (not) the only option" when you have three officers responding to subdue a slim, mentally ill teenager.

"Every other opportunity to resist using that deadly force should be deployed (first)," said O'Mara. "Why not just back away from the situation and see what happens?"

Yet some criminal experts say it may not be that simple. Law enforcement officers thrust into situations like this do have protocols to follow. They often do have nonlethal tools like Tasers at their disposal. But things don't always go to plan; in fact, things oftentimes go wrong, forcing an officer to make extremely difficult, split-second decisions whether to use lethal force or not.

"They have to make a judgment very quickly: Is (the individual) a danger to themselves or a danger to others?" said Ron Martinelli, a justice and forensic consultant who trains police officers on what to do in such situations.

The lawyer for Bryon Vassey -- the Southport, North Carolina, police detective who fired the fatal shot in this instance -- said firmly that his client made the correct, spur-of-the-moment decision.

"At the instant that it occurred, he had to make that (judgment call) in that split instant," W. James Payne told CNN.

'Objective reasonable' to use force?

Investigators and, possibly, a civil or criminal jury will decide whether Detective Vassey did the right thing.

Already, two law enforcement departments have weighed in, determining that their officers didn't break the law or policy. The Southport police department put Vassey on paid administrative leave, a step that John Midgette, the head of the North Carolina Police Benevolent Association, says is standard in such cases.

That department's police chief, Jerry Dove, says Vassey has a spotless record but, still, he's "waiting for when I hear all the inquiries." Those are being conducted by the state Bureau of Investigation and chief prosecutor for the state's 13th Judicial District, with the latter possibly pressing charges.

Experts say the final judgments likely will hinge on whether Vassey acted in an "objectively reasonable" matter. That term comes from a 1989 Supreme Court ruling, Graham v. Connor, and means that an officer -- and ultimately, higher authorities -- must decide on the spot whether there is a valid presumption of an imminent, serious risk that would warrant the use of force.

"It's objectively reasonable as seen by the officer," said Martinelli, a former officer who adds there's no federal legal requirement that officers use "the least intrusive level of force" nor do they "have to put themselves at risk." "And it often all depends on a rapidly evolving situation."

David Klinger, a ex-patrol officer who now teaches at the University of Missouri-St. Louis, explains "notions of reasonableness are predicated on the circumstances." Even then, different law enforcement officers working alongside each other may well reach opposite conclusions on whether someone poses a real threat and should be fired upon, noted Klinger, an expert in officer-involved shootings.

In the Boiling Spring Lakes case, there were three different officers at the scene. The first two didn't open fire, but Vassey did.

Vidal was making a "stabbing motion to an exposed part" of another officer -- wearing a bulletproof vest -- struggling with him, said the detective's lawyer. But this downed officer didn't yell out, asking for help or someone to shoot, according to Payne.

O'Mara said it doesn't make sense to him that shots needed to be fired after Vidal had been tased and given he was outnumbered by the three officers in the room, including two that Vidal's family claimed had him pinned down.

Ultimately, it won't matter what outside experts, Detective Vassey or even the late teen's family think is "objectively reasonable" in this case.

Speaking generally about cases like these, University of North Carolina-Charlotte criminology professor Vivian Lord said, "It's up to the courts to make a decision on whether or not they agree with that."

Three officers, all from different agencies

It may be notable, too, that the three officers who responded all came from different agencies.

Especially in small towns, having one officer from another agency like a sheriff's department come to a scene isn't unusual, said Lord. Typically, she adds, the first responding officer and one from the home agency -- in this case, from Boiling Spring Lakes police -- acts as the lead officer.

But Vidal's stepfather Mark Wilsey -- who, along with the late teen's mother, witnessed the incident -- said the Southport detective was assertive when he came in, disrupting the situation.

"(He) walks in the room, walks around the corner, (and) says, 'We don't have time for this. Tase that kid now. Let's get him out of here,'" Wilsey said, according to CNN affiliate WWAY

Authorities have not confirmed that such a statement was made, or that this detective by himself made the situation worse.

Still, Martinelli said generally -- even if every officer did everything right -- issues can arise when there are officers not used to working together due to differences in style, training or perspective.

"When you have multiple jurisdictions involved, it's very difficult to communicate," he said. "It's not unusual for one officer to act one way, and another officer to act another way."

The significance of late teen's schizophrenia

Photos: Photos: 'He was a good kid' Photos: Photos: 'He was a good kid' Teenager Keith Vidal was shot and killed Sunday. Keith's stepbrother, Mark Ryan Wilsey, said he was in "absolute panic" when his parents called to tell him the news. "I thought I needed to get to my brother's side and protect him from anyone who may harm him." Hide Caption 1 of 4 Photos: Photos: 'He was a good kid' Keith Vidal with his mother, Mary Wilsey. Vidal had schizophrenia, but "he was a good kid. He was in school," said his stepbrother, Mark Wilsey.

Hide Caption 2 of 4 Photos: Photos: 'He was a good kid' Mark Wilsey called Vidal his "little buddy." He said they did everything together, from hunting and fishing to golfing and playing basketball. Hide Caption 3 of 4 Photos: Photos: 'He was a good kid' Keith Vidal with his older brother, Joey Vidal. Hide Caption 4 of 4

And when officers respond to deal with a mentally ill person, any disruption can have a snowball effect, experts say.

The 911 caller made clear Vidal had schizophrenia, adding he "won't take his medication," was carrying a screwdriver and wanted "to fight his mother." Vidal's stepbrother, Mark Ryan Wilsey, told CNN that local police were familiar with him, having come to the house at least three times before.

"He's not doing very good," said the man on the 911 call. "We've got to get him someplace."

According to O'Mara, the fact this was a call for help -- to subdue someone and get him to a professional -- is significant.

"They have to respond with that in mind," said the Florida-based lawyer. "... They have to look at the situation as not being a criminal (matter), but as being (to help) someone who is ill."

It is also important to note someone who suffers from a mental illness like schizophrenia may not act rationally; he or she may seem to communicate coherently and appear composed one moment, only to spiral out of control the next.

"It doesn't take a whole lot," said Lord, a licensed psychologist, who made a point to add schizophrenics aren't necessarily violent. "If somebody is calming down, ... anything changing could make that happen."

Within 70 seconds -- according to police records cited by CNN affiliate WECT -- of when the Southport detective arrived, things went downhill quickly, ending in Vidal's death.

The detective didn't necessarily have to do or say anything to set off this spiral. Martinelli -- who said he specializes in handling what authorities call emotionally disturbed people, or EDPs -- said anyone coming into a room and distracting a mentally ill person "could be like throwing gas on a flame."

Adds Lord, "If (a mentally ill individual) is unstable, it's hard to say what might have made this blow back up."

Justified or not?

Vidal's stepbrother said the first two officers to arrive "did nothing wrong."

"All they did was tase my brother and try to get him into handcuffs so he couldn't harm himself," said Mark Ryan Wilsey, who wasn't at the scene but relayed his family's account. "They had the situation under control."

The family lays the blame squarely on the Southport detective.

"This officer who shot my son needs to be behind bars," said Vidal's mother, Mary Wilsey. "He needs to die the way my son died."

The detective spoke moments after the shooting, saying on a radio call, "I don't know if you've been advised or not, but shots fired. I've had to defend myself against the subject."

His story later changed, with his lawyer and the North Carolina Police Benevolent Association saying the shots were fired to defend another officer. O'Mara said he believes the altered story might come back to hurt Vassey.

The benevolent association is siding squarely with the detective, concluding after talking with two of the officers involved that the teen posed a "deadly threat."

"We are very confident that the officers did what they should have under state law," Midgette, the trade group's director, told CNN. "It's a very tragic situation, but we do believe the officer."