Gunman (stock)
Gunman (stock)iStock

The parents of a 15-year-old who shot dead four students at a US high school with a gun bought by his father pleaded not guilty to involuntary manslaughter on Saturday, as a Michigan judge set a combined million-dollar bond for their release, AFP reports.

James and Jennifer Crumbley, the parents of shooting suspect Ethan Crumbley, were arrested overnight after police tracked them down in an industrial building in Detroit, located 40 miles (65 kilometers) from the shooting in Oxford.

The pair were considered fugitives -- having reportedly withdrawn $4,000 in cash and switched off their phones -- although the Crumbleys' lawyers told the court their clients "were absolutely going to turn themselves in."

However, Sheriff Michael Bouchard of Oakland County -- where the shooting took place -- told reporters during a news conference Saturday that it appeared the couple had help in "hiding" from police.

"They weren't looking toward surrendering at that point," he said, adding, "We believe they were assisted in that location, to get there, to get in."

At their arraignment, Judge Julie Nicholson set bond at $500,000 for each parent, calling the charges "very, very serious" and saying "the court does have some concern about the flight risk."

Four students, aged 14 to 17, were killed in the Tuesday shooting at Oxford High School north of Detroit and six more were wounded, along with a teacher.

The couple's son, Ethan, has been charged as an adult with state murder and terror charges, while his parents each face four counts of involuntary manslaughter -- each carrying a sentence of up to 15 years in jail.

In announcing charges against the boy's parents on Friday, Oakland County prosecutor Karen McDonald said the rare move was intended to "send the message" that gun owners have a responsibility.

The parents are accused not only of supplying their son with a weapon, but of ignoring escalating warnings that he appeared to be on the brink of violence, including on the day of the shooting.

Four days before the tragedy, James Crumbley bought the 9mm Sig Sauer semi-automatic handgun for his son, McDonald told the judge at Saturday's hearing.

His wife took their son to a shooting range the following day, posting on social media that she had bought a gun for her "baby" for Christmas, the prosecutor said.

The Crumbleys' lawyer, Shannon Smith, told the judge it was "absolutely not true" that Ethan Crumbley had free access to a gun.