Detroit police said early on Saturday that James and Jennifer Crumbley, had been arrested, after the pair earlier appeared to have left town.

Michigan prosecutors on Friday charged the couple with involuntary manslaughter for buying their son a handgun as a Christmas gift and ignoring warning signs as late as the day of the shooting.

They said Jennifer Crumbley wrote in a text message to her son, "LOL, I'm not mad at you. You have to learn not to get caught," after a teacher saw him searching for ammunition on his phone during class.

The morning of the shooting, it's alleged a teacher discovered a drawing that Ethan Crumbley had made depicting a handgun, a bullet, and a bleeding figure, with the words "Blood everywhere" and "The thoughts won't stop - help me." After being summoned to the school and shown the picture, James and Jennifer Crumbley did not take their son home, search his backpack or ask about the gun, prosecutors said.

The Crumbleys' lawyers, Shannon Smith and Mariell Lehman, on Friday denied reports that their clients were fleeing law enforcement.

The case appears to be the first against parents of an alleged teenage school shooter.

Some states have laws holding gun owners liable for failing to secure weapons around children, but Michigan does not. That means prosecutors will be relying on traditional criminal law, under which they must prove that the Crumbleys were not merely negligent, but grossly negligent or reckless, experts say.

Ethan Crumbley has been charged as an adult, even though he is under 18.

While other parents have been charged for deaths resulting from unsecured guns, those cases have involved much younger children.

Robert Leider, a professor at George Mason University's Antonin Scalia Law School, said those cases were different from the Crumbleys' because young children legally cannot have criminal intent.

"Here you have a teenager who can form his own criminal intent," Leider said. "That weighs in favour of breaking the chain of causation" between the Crumbleys and the shooting.

Eric Ruben, a professor at Southern Methodist University's Dedman School of Law, said a case focusing on what the Crumbleys did - like buying the gun despite knowing it posed a high risk - is likely stronger than one homing in on what they failed to do.

Michigan law prohibits those under age 18 from buying or possessing firearms, except in limited circumstances such as hunting with a license and a supervising adult.

Ruben said the parents would likely defend themselves by arguing that they could not have reasonably foreseen that their actions would lead to the shooting, meaning they could not be responsible for causing it.

Australian Associated Press