Dec 3 (Reuters) - Prosecutors filed involuntary manslaughter charges on Friday against the parents of the Michigan teenager who authorities say fatally shot four classmates at his school earlier this week.

James and Jennifer Crumbley each face four manslaughter counts, three days after police say their 15-year-old son, Ethan, opened fire at Oxford High School, about 40 miles (60 km) north of Detroit, killing four students and wounding seven others.

James Crumbley brought Ethan along with him when he purchased the handgun used in the attack four days prior, prosecutors said.

When he heard reports of a shooting at the school, James Crumbley immediately drove home to look for the gun, which was missing, Oakland County Prosecutor Karen McDonald told a news conference on Friday. Crumbley then called authorities to say he suspected his son may be the shooter.

Parents are rarely charged in connection with children's school shootings. Unlike some states, Michigan does not legally require gun owners to keep their firearms secured from children.

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The attack was the deadliest school shooting this year, according to Education Week, and marks the latest in a decades-long string of mass shootings at U.S. schools.

Prosecutors described in chilling detail drawings and writings made by the gunman suggesting the possibility that he was planning a shooting rampage.

The day before the shooting, a teacher found a note with a drawing of a gun and blood from Crumbley, McDonald said. Authorities have previously said school officials met with him and his parents the morning of the attack to discuss concerns about his behavior.

"Any individual who had the opportunity to stop this tragedy should have done so," McDonald said when asked whether school officials should have done something. (Reporting by Brendan O'Brien and Joseph Ax; Editing by Daniel Wallis)