A jury found James Crumbley guilty of involuntary manslaughter on Thursday after about 11 hours of deliberation, holding him partially responsible for failing to prevent his son from carrying out Michigan’s deadliest school shooting.

Mr. Crumbley’s wife, Jennifer, was convicted of identical charges last month in the same Pontiac, Mich., courtroom, with the same judge presiding. The trials became a lightning rod for issues of parental responsibility at a time of high-profile gun violence by minors.

The parenting skills of each defendant came under intense scrutiny, as did the shooter’s access to a handgun that his father had purchased. Now, two separate juries have taken the unusual step of holding a parent criminally responsible for a child’s horrific crimes. Each faces a maximum of 15 years in prison.

Oakland County prosecutors charged the Crumbleys three days after the Nov. 30, 2021, shooting at Oxford High School, where their son, Ethan, who was 15 at the time, killed Madisyn Baldwin, 17; Tate Myre, 16; Justin Shilling, 17; and Hana St. Juliana, 14, and injured seven others.

“James Crumbley was presented with the easiest, most glaring opportunities to prevent the deaths of these four students,” Karen McDonald, the prosecutor in Oakland County, said in closing arguments on Wednesday. “And he did nothing.”

Mariell Lehman, Mr. Crumbley’s defense lawyer, urged the jury to take into account how much Mr. Crumbley could not have known until it was too late. “You heard no testimony, and you saw no evidence, that James had any knowledge that his son was a danger to anyone,” she said.