Harlan Drake shattered a television and used the broken glass to cut his arm, Sheriff George Braidwood said.
Staff at the Shiawassee County jail had been checking Harlan Drake every 15 minutes and responded Saturday when they heard the TV break, Braidwood said. Drake was treated at a hospital and returned to the jail Saturday night, he said.
"Since then he's been fine. He's been cooperative. He's been very passive," Braidwood said.
Drake, 33, is charged with first-degree murder in the fatal shootings of James Pouillon and Mike Fuoss. He was arrested Friday.
Pouillon, 63, was a well-known abortion protester in Owosso, 70 miles northwest of Detroit. He was gunned down in a drive-by shooting while holding a sign near the high school. Authorities say Drake was angered by the graphic image of an aborted fetus.
Fuoss, 61, was subsequently shot at his gravel company, just outside Owosso. Investigators say Drake's mother once worked there, but they're not certain how that fits into a possible motive.
Authorities say Drake disclosed plans to pursue a third target, real-estate agent James Howe. Drake's mother also had worked with Howe.
Drake likely will have an attorney assigned to his case Monday.
President Barack Obama called Pouillon's killing "deplorable" on Sunday, the same day more than 200 people attended a vigil near the site where he was shot.
By Associated Press Writer Tim Martin