Police have issued a warning to the parents of a 15-year-old boy who shot dead four fellow high school students who left town after they were charged with involuntary manslaughter. 

James and Jennifer Crumbley, the parents of Ethan Crumbley, were each charged with four counts of involuntary manslaughter today over the shooting in the northern US state of Michigan. 

But shortly after they were charged, police sought assistance locating the couple who were declared missing. 

"If they think they are going to get away, they are not," Sherriff Michael Bouchard told CNN. 

Asked if the Crumbleys were "missing now", Sherriff Bouchard replied: "Correct." 

"The action of fleeing and ignoring their attorney certainly adds weight to the charges. They cannot run from their part in this tragedy," he added in a statement. 

Lawyers for the Crumbleys have since denied they are fugitives, saying they left town "for their own safety" and are returning soon. 

A prosecutor says the parents of a teen accused of killing four students at a Michigan high school were summoned a few hours earlier after a teacher found a drawing of a gun, a person bleeding and the words "help me". 

Oakland County prosecutor Karen McDonald made the disclosure on Friday as she filed involuntary manslaughter charges against Jennifer and James Crumbley, the parents of 15-year-old Ethan Crumbley. 

McDonald says the gun used in the shootings at Oxford High School was purchased by James Crumbley a week ago and given to the boy. 

Ethan Crumbley was returned to his classroom and later emerged from a bathroom, firing a gun at students. He's charged with murder and other charges. 

McDonald says Jennifer Crumbley sent her son a text, saying "Ethan, don't do it." 

The prosecutor filed the involuntary manslaughter charges after saying earlier that the parents' actions went "far beyond negligence". 

Jennifer and James Crumbley were charged with four counts of involuntary manslaughter. Under Michigan law, an involuntary manslaughter charge can be pursued if prosecutors believe someone contributed to a situation where harm or death was high. If convicted, they could face up to 15 years in prison. 

"The parents were the only individuals in the position to know the access to weapons," Oakland County prosecutor Karen McDonald said on Thursday. The gun "seems to have been just freely available to that individual". 

Ethan Crumbley, 15, has been charged as an adult with two dozen crimes, including murder, attempted murder and terrorism, for the shooting on Tuesday at the high school in Oakland County, roughly 50km north of Detroit. 

Four students were killed and seven more people were injured. Three were in hospitals in stable condition. 

The semi-automatic gun was purchased legally by Crumbley's father last week, according to investigators. 

Parents in the US are rarely charged in school shootings involving their children, even though most minors get guns from a parent's or relative's house, according to experts. 

There's no Michigan law that requires gun owners keep weapons locked away from children. McDonald, however, suggested there's more to build a case on. 

"All I can say at this point is those actions on Mom and Dad's behalf go far beyond negligence," she told WJR-AM. "We obviously are prosecuting the shooter to the fullest extent ... There are other individuals who should be held accountable." 

Later at a news conference, McDonald said she hoped to have an announcement "in the next 24 hours". She had firmly signalled that Crumbley's parents were under scrutiny when she filed charges against their son on Wednesday. 

Sheriff Mike Bouchard disclosed Wednesday that the parents met with school officials about their son's classroom behaviour just a few hours before the shooting. 

McDonald said information about what had troubled the school "will most likely come to light soon". 

Crumbley stayed in school Tuesday and later emerged from a bathroom with a gun, firing at students in the hallway, police said. 

Late on Thursday the superintendent for the district posted a YouTube video where he said the teenager was called to the office before the shooting but "no discipline was warranted". 

Tim Throne, leader of Oxford Community Schools, said the high school looks like a "war zone" and won't be ready for weeks. But he repeatedly credited students and staff for how they responded to the violence. 

"To say that I am still in shock and numb is probably an understatement. These events that have occurred will not define us," Throne, grim-faced and speaking slowly, said in the 12-minute video. 

"I want you to know that there's been a lot of talk about the student who was apprehended, that he was called up to the office and all that kind of stuff. No discipline was warranted," Throne said. "There are no discipline records at the high school. Yes this student did have contact with our front office, and, yes, his parents were on campus November 30." 

Throne said he couldn't immediately release additional details. 

By - Associated Press