Owosso, Mich. ? A man carrying grudges against several people set off on a shooting spree Friday morning, authorities said, killing an abortion protester outside a high school because he didn’t like the activist holding a sign with graphic images of a fetus in front of students.

The gunman drove next to a gravel pit business and shot and killed the owner, who apparently also upset him, police said. Authorities believe they stopped a third slaying by catching up with the gunman before he could kill again.

“The defendant had ill will toward these three individuals — not for the same reason necessarily, but had a grudge,” said Shiawassee County Prosecutor Randy Colbry.

Police charged Harlan James Drake, 33, with first-degree murder. He was arraigned by video without an attorney and ordered held without bond. Authorities said he was a truck driver who mostly lived on the road in his cab and had family in the area, but they were mystified by what may have led him to kill.

“Out of a two-month period, he might be here for two days. We have no history of local contact with him,” said sheriff’s Detective Lt. David Kirk. “It becomes a mystery to us why today all of this transpired.”

The shootings started around 7:20 a.m. across the street at Owosso High School, as parents dropped off students before class. James Pouillon, a well-known activist in the town, was standing across the street with a sign that pictured a chubby-cheeked baby with the word “LIFE” on one side and an image of an aborted fetus with the word “ABORTION” on the other.

Pouillon, known as “the sign man” for his years of in-your-face protests against abortion, was a polarizing figure in Owosso, a town of 15,000 best known as the birthplace of 1948 Republican presidential candidate Thomas Dewey. While inhaling oxygen from a small tank, he could usually be seen with his anti-abortion signs outside schools, the library, city hall, even football games.

“His dedication to his cause was unprecedented,” said Tony Young, who tangled with Pouillon during protests outside his car dealership.

The county’s chief assistant prosecutor, Sara Edwards, said there didn’t appear to be a “triggering event” but Pouillon’s presence outside the school seemed to aggravate Drake. It was “the fact that he was outside the high school with his signs in front of children going to school,” she said.

The shots came as students and some horrified parents and students watched. The gunman fired several shots from the window of his vehicle as he drove past the school, authorities said.

Drake then drove seven miles and down a dead-end country road to Fuoss Gravel Co. and killed Mike Fuoss, 61, who owned the gravel business, said Shiawassee County Sheriff George Braidwood. The two men knew each other, but authorities didn’t detail what may have led to his slaying.

Lisa Merkel, Fuoss’ sister-in-law, said other family members told her that the suspect’s mother worked at the gravel company more than a decade ago.

Someone wrote down Drake’s license plate number after Pouillon’s shooting and called police, who arrested him before he could fulfill a plan to kill a third man in town, Colbry said. Drake told authorities he was involved in Fuoss’ slaying when they questioned him, authorities said.