NEWAYGO, Mich. (AP) — In March, a teen accidentally detonated a homemade explosive at a school in western Michigan.

Now his father is going to prison for four years.

David Saylor Sr. was sentenced by a federal judge in Grand Rapids.

In March, Saylor’s son brought a homemade explosive to Newaygo High School and accidentally detonated it, injuring himself and others. The teen lost both thumbs.

Authorities subsequently searched Saylor’s home and filed charges. He pleaded guilty to possession of a pipe bomb and a stolen gun.

Saylor admitted that he and his son designed and made explosives for two years.