The prosecutor overseeing the investigation into a mass killing at a Michigan high school this week strongly suggested Wednesday that she would charge the teenage suspect’s parents, an unusual move but one that gun control advocates say is essential to combating the nation’s scourge of shootings by minors.

Officials have said that the father of the suspect, 15-year-old Ethan Crumbley, bought the semiautomatic handgun used in the killings last Friday. Just four days later, on Tuesday, Crumbley forged a path of terror at Oxford High School, killing four people and injuring seven others, Oakland County Prosecutor Karen McDonald said.

While it is unclear how Crumbley may have obtained the gun from his father, McDonald said Wednesday that gun owners have a responsibility to secure their weapons — particularly when young people are involved.

“Those who do not do that should and will be held accountable,” she said. “We have to do better.”

McDonald said in addition to charges announced Wednesday against the teen — including four counts of first-degree murder — she expected that other charges could be filed, including against Crumbley’s parents.

Such a charge would be a rarity: Adult gun owners are almost never held accountable when children use their weapons to harm themselves or others.

That’s despite the fact that if children as young as 6 did not have access to guns, well more than half of the country’s school shootings since 1999 would never have happened, according to an analysis by The Washington Post.

“If you look at school shootings, the overwhelming majority are committed by students, and the overwhelming majority of those students have guns that they brought from their homes or a relative’s home,” said Daniel Webster, director of the Johns Hopkins Center for Gun Violence Prevention and Policy.

While school shootings remain rare, there have been more in 2021 — 34 — than in any year since at least 1999, according to a Washington Post database that tracks acts of gun violence on K-12 campuses during regular school hours.

This year’s total has eclipsed the previous record, of 29 from three years ago, despite most students not attending school for the first two months of 2021 — and a full month remaining before year’s end. Targeted attacks, most often sparked by fights between students, have driven the spike in on-campus gun violence since March.

In schools across 22 states, at least 45 people have been shot, and nine of them were killed. This year’s shootings alone have exposed about 27,000 students to gun violence, bringing the total since 1999 to 278,000.

Tuesday’s mass killing in Oxford, about an hour’s drive from Detroit, was the deadliest school shooting in more than three years.

Oakland County Sheriff Michael Bouchard said Wednesday that Crumbley “wasn’t on any law enforcement radar that I’m aware of” before the shootings. But there were problems in the immediate lead-up to the attack: Bouchard said that, on Monday, school officials met with Crumbley to discuss “concerning behavior in the classroom.”

On Tuesday morning, Crumbley’s parents were summoned to the school for a meeting at which the teen was present. Bouchard, who did not elaborate on the nature of the issues being discussed, said that early that afternoon, Crumbley went to the bathroom and emerged wielding the handgun. As he walked the hallways, he began firing “methodically and deliberately” at his fellow students at close range, prosecutors said.

A judge ordered Crumbley held without bail at a Wednesday arraignment. He did not enter a plea, so a not-guilty plea was entered on his behalf. His parents, James and Jennifer Crumbley, appeared side-by-side in a virtual appearance before switching off their cameras for the remainder of the hearing.

Ethan Crumbley’s attorney did not immediately respond to a request for comment.

Prosecutors have not said what they believed may have motivated the teen, but McDonald said a “mountain of evidence” indicated that the shooting was premeditated.

“It isn’t even a close call,” she said.

Lt. Tim Willis of the Oakland County Sheriff’s Office said at Wednesday’s court hearing that Crumbley had recorded a video the night before the shooting in which he discussed killing students.

Officials said they were also looking at social media posts by the teen in the days leading up to the shooting. In one that appeared to have been posted on Crumbley’s Instagram account last Friday, a picture of a hand cradling a gun was captioned: “Just got my new beauty today. SIG SAUER 9mm. Ask any questions I will answer.”

While Crumbley’s account has been deleted, screenshots of the post circulated widely. Officials have previously said that a SIG Sauer 9mm was the murder weapon and that they were reviewing social media posts that showed Crumbley with such a gun.

McDonald would not provide details Wednesday when asked whether the handgun purchased by Crumbley’s father had been locked or secured in any way at the family’s home. But she said that gun owners have a responsibility to keep their weapons out of the hands of minors, who are barred from possessing guns in Michigan.

It is not clear under what statute Crumbley’s parents would be charged, if they are.

Michigan law does not require gun owners to lock up their weapons or keep them away from children, according to Giffords Law Center. Even in the 30 states that have passed some form of a child access protection law, researchers say, the statutes are often not enforced, or are too limited or carry weak penalties, rendering them ineffective.

While investigators don’t always determine — or publicly reveal — the weapons’ origins when they are fired by a child, The Post identified and reviewed 105 cases between 1999 and 2018 in which the source was identified.

Of those, the guns were taken from a child’s home or those of relatives or friends 84 times. The Post discovered just four instances in which the adult owners of the weapons were criminally punished because they failed to lock them up.

None of the four successful prosecutions identified by The Post resulted from charges related to negligent-storage laws. The harshest penalty among those cases was a 29-month term behind bars for involuntary manslaughter. In that instance, a man in Michigan used a shoe box to store his .32-caliber semiautomatic handgun, which a 6-year-old visitor found and took to school, then fatally shot a first-grade classmate.

McDonald called Wednesday for laws to be strengthened to better address gun access issues among minors. “How many times does this have to happen?” she asked in what has become a familiar refrain following school shootings.

But such toughening of the rules has been fiercely resisted by gun rights groups such as the National Rifle Association. Bouchard, the sheriff, said Wednesday that prosecutors aren’t adequately using the gun rules they already have, often dropping charges on crimes such as possession.

“We have a whole lot of gun laws that are meant to hold criminals accountable. And they’re not utilized,” he said.

Even gun control proponents acknowledged that a change in legislation can only do so much.

“Laws,” said David Chipman, a veteran Bureau of Alcohol, Tobacco, Firearms and Explosives agent once nominated to lead the agency, “can help hold people accountable for contributing to reckless harms. But it will take community pressure to ensure that irresponsible gun owners stop being shielded as patriots by gun extremists and rather called out as the pariahs that they are, especially by fellow, responsible gun owners.”

While details of the Crumbley gun purchase were not immediately clear Wednesday, Webster noted that gun sales have surged since the beginning of the pandemic or possibly just before.

Many people are buying guns with the goal of protecting themselves from danger, even though it’s much more common that someone purchases a gun and “an underage youth gets their hands on it and hurts themselves or others,” Webster said.

Active shooters usually get their guns legally and target places they already know, according to an FBI study that looked at dozens of different attacks. The FBI study found that these attackers often displayed numerous red flags and warning signs that were noticeable beforehand, which included expressing a desire to harm people.

“Usually,” Webster said, “these things don’t come out of the blue.”

john.cox@washpost.com

mark.berman@washpost.com