(CNN) A pair of experts at a pretrial hearing for the parents of Michigan school shooter Ethan Crumbley should be allowed to testify before a jury to dispel the myth mass shootings can't be prevented, a prosecutor said Friday.
Jennifer and James Crumbley have each been charged with four counts of involuntary manslaughter after prosecutors accused them of giving their son easy access to a gun and ignoring signs he was a threat before last year's shooting at Oxford High School that resulted in four deaths and seven injuries.
"Both experts testified unequivocally there is a clear pathway to violence, that school mass shooters don't just snap and that school mass shootings can be prevented," Oakland County Chief Assistant Prosecutor David Williams told the court after both experts took the stand.
"It is undisputed that school mass shooters give signs ... and that school mass shootings ... don't come out of the blue."
Prosecutors want to introduce testimony from the experts to show the tragedy could have been averted with proper intervention. The state has said the parents exposed their son to years of "chaotic, toxic conflict," and that they left him in an unstable home often with little supervision, creating a pathway to violence.
Williams argued the expert testimony would ensure jurors don't labor under what he called the "common misconception" that mass shootings are not preventable.
The defense acknowledged the witnesses as experts but disputed the reliability of their studies and the relevance of their conclusions in this particular case.
Judge Cheryl Matthews said she expects to issue a written opinion on the matter in the next week to 10 days. The Crumbleys trial is expected to start on January 17.
The first expert, Jillian Peterson, a forensic psychologist, testified in the Oakland County courtroom that mass shooters have "a slow build towards violence over time" and they "give off lots of warning signs."
"In studying mass shooters we found that there is a consistent pathway up to a mass shooting," Peterson testified.
"They don't just snap," she added.
Peterson testified her research has shown a "consistent pathway" to violence "that often started with early childhood trauma," including "physical or sexual abuse, a chaotic household, neglect."
"There was this slow build over time up to what we called a crisis point," said Peterson, an associate professor of criminology and criminal justice at Hamline University. "That crisis point is often a suicidal crisis where the perpetrator is hopeless and isolated and no longer cares if they live or die. During that crisis point their behavior is changing, they're acting differently and the people around them are noticing that they are acting differently."
That slow build often involves shooters "studying other perpetrators" -- which is known as "social proof," she testified, adding that shooters "look for models of behavior, often times they identify with previous shooters and see themselves in those previous shooters."
Peterson said shooters often leak their plans and violent intentions, access guns and determine a location that represents "their grievances with the world."
Peterson identified what she said were two "crisis points" ahead of the Oxford High shooting. She defined crisis points as the moment when "current circumstances are overwhelming your ability to cope. Something pushes you over the edge. It could be the loss of a job, the loss of a relationship, and then you start acting differently."
In March of last year, Peterson testified, Ethan Crumbley spoke "about potential hallucinations, delusions, needing mental health care, even thinking about calling 911 on himself in order to get mental health care."
The second point, she said, came in the month before the shooting, when his behavior was changing.
"His best friend had been sent away. I believe his dog had died. He was acting differently during that period as well," Peterson testified.
The teen's journal also "indicated he was in crisis," she said.
Shooters in crisis typically exhibit "increased agitation and isolation" as well as abusive behavior, Peterson testified. They don't turn in homework assignments and miss school.
"We've discovered that leakage is a really critical intervention point," she said. "Leakage is really a cry for help and so that becomes the key point where someone needs to intervene."
Under questioning by the defense, Peterson said she had no evidence the Crumbleys saw writings or text messages in which their son hinted at violence.
"A jury of laypeople isn't going to need the testimony of an expert to label for them the steps on the pathway to violence," said attorney Mariell Lehman, who represents James Crumbley, 46. "They should see an object or a piece of writing and know that it's concerning without being told that it's concerning."
Attorney Shannon Smith, representing Jennifer Crumbley, 44, called the expert testimony a "veiled attempt" to accuse the parents of gross negligence.
"That really is a question that has to solely go to the jury," Smith said.
A second expert, Dewey Cornell, a forensic psychologist who teaches at the University of Virginia, testified that all mass shootings can be prevented under an approach known as "threat assessment." He said parents are key in that assessment.
"Parents are the greatest influence, the greatest knowledge, have the greatest ability to intervene and responsibility for their children," he testified.
Using lightning as an example, Cornell noted there is a difference between prediction and prevention.
"We can't predict where lightning will strike, but we know that we don't want to get in a swimming pool during a storm," he told the court. "We know that we don't want our kids getting in the swimming pool during a storm. So you can avoid something that you can't really predict."
Williams told the court the jury should hear from the experts that mass shootings are not inevitable.
"We are not helpless and we don't have to just live with them. They are preventable," he said.
Prosecutors, in court filings, had argued that evidence of the teen's parents' personal problems, including an extramarital affair and substance abuse, should be introduced at their trial.
"Every time, judge, there's another shooting ... there's always someone who says, 'There were no signs,' " Williams told the court Friday. "And every time it turns out to be wrong. There are signs and the jury needs to hear that, and understand people don't just snap so that they can evaluate whether these defendants, in fact, could have prevented the shooting."
The parents have pleaded not guilty, and their attorneys had argued in court documents the charges have no legal justification and the couple should not be held responsible for the killings their son committed. It's possible the teen may be called as a witness in his parents' case, according to his attorney.
At the start of the hearing, the couple told the judge they agreed to a joint representation conflict waiver. The Crumbleys, in black-and-white and orange jumpsuits, sat at the defense table, separated by their attorneys.
Their 16-year-old son, Ethan, pleaded guilty Monday to one count of terrorism causing death, four counts of first-degree murder and 19 other charges stemming from the November 30 mass shooting at Oxford High that killed Madisyn Baldwin,17; Tate Myre,16; Hana St. Juliana,14; and Justin Shilling,17.
James Crumbley purchased the gun used in the shooting just four days before the deadly attack, prosecutors have said.
Ethan Crumbley, who was 15 at the time of the shooting, previously had pleaded not guilty to the charges but changed his plea at Monday's hearing. His defense team previously had filed a notice of an insanity defense for the teen but ultimately decided a guilty plea was in his best interest, attorney Paulette Michel Loftin said.