CHICAGO (NewsNation Now) — The U.S. Secret Service says that in nearly all mass shootings, the shooter gave some kind of warning sign.

The agency’s National Threat Assessment Center found that “individuals contemplating violence often exhibit observable behaviors” such as mental health issues, disciplinary issues in school or disputes with law enforcement and adverse childhood experiences.

Nineteen states have red flag laws in place to allow police or family members to petition a court to order the temporary removal of firearms from a person who may present a danger to themselves or others.

A judge then will decide to grant or deny the petition to remove guns and ban new firearm purchases. Although the judge has the final say, the person involved can appeal the request.

Max Schachter advocated for the red flag law in Florida after his son, Alex, was killed in the 2018 mass shooting at Marjory Stoneman Douglas High School in Parkland. The law was passed with bipartisan support. Schachter said he wishes states including Michigan could have implemented the law before the deadly mass school shooting that happened Tuesday.

“I think every state should have a red flag law,” he told NewsNation’s Brian Entin. “If we know that someone is thinking about hurting themselves or others, due to this law we have the ability to get a court order and remove that dangerous weapon from the situation.”

The suspected gunman in the Oxford, Michigan High School shooting, 15-year-old Ethan Crumbley, is being charged as an adult for killing four fellow students and injuring seven others.

Schachter said when saw the images on the news, he couldn’t believe it.

“Oh, my heart sank, he said. “I feel horrible for these families, three and now we just had a fourth victim pass away.”

He noted that unlike Parkland, Michigan deputies took down the shooter in just two minutes, which is something Schachter said he’s proud about.

“When they confronted the shooter and they got him to surrender, he had seven bullets in his gun. Those bullets would have been more injured and more casualties and (police) saved lives.”

Oakland County Sheriff Michael Bouchard told reporters at a Wednesday news conference that the suspect “had been involved in a meeting over behavior issues the prior day and the morning of the shooting. Bouchard wouldn’t discuss details of the behavior school officials were concerned about, but said Crumbley was at the meeting.

In several states, law enforcement has credited the red flag law with preventing mass shootings. President Joe Biden recently included a directive to create a model red flag law for other states to pass.