The father of Michigan high school Ethan Crumbley, has been found guilty on all 4 counts of involuntary manslaughter ... just weeks after his wife Jennifer saw the same verdict.

The jury reached the decision for James Crumbley Thursday after 1 day of deliberations. His sentencing is scheduled for April 9, the same date as his wife.

With this verdict, Crumbley was found to be negligent for disregarding warning signs exhibited by his son that could have potentially prevented the devastating event. Prosecutors said he even purchased a gun for his son just days before he used it to open fire at Oxford High School in the Detroit suburb of Oxford Township, MI, in November 2021, killing 4 students.

The verdict comes a few weeks after his wife Jennifer's conviction -- which marked an historic moment, as it's unprecedented for a parent to be criminally charged in connection with their child's involvement in a mass shooting.

Jennifer's testimony during her trial had shed light on the role she says her husband, James, played in the tragic events ... saying he had purchased the gun their son used in the shooting and was the one responsible for hiding it.

She also testified she was aware her son was struggling but had no inkling he was capable of carrying out a mass shooting ... saying if she had known, she'd done the whole thing differently.

17-year-old Ethan was sentenced to life in prison without the possibility of parole back in December.