Turlock, Calif. ? A crazed man parked on a dark country road Saturday night, took a baby boy from the car seat in his pickup and beat the child to death until a Modesto police officer, dropped on the scene by helicopter, shot the man dead, authorities said.

Passersby calling 911 at 10:13 p.m. PDT described a horrific scene on West Bradbury Road near the intersection of South Blaker Road in rural Stanislaus County. At least one tried to stop the attacker, who swung and slammed the child into the asphalt behind his parked four-door Toyota pickup.

“In the shadows and light it looked like he had hit an animal,” said Dan Robinson, the chief of Crows Landing Volunteer Fire Department, who came upon the chaos driving home from a late dinner in Turlock. “As we backed up again, I could see that he had blood on his arms. I could see that it was a small child.”

Robinson jumped from his vehicle and confronted the man, who lunged at him. Robinson said the man wasn’t screaming and wasn’t loud, but was forceful, saying “demons” were in the boy.

A Stanislaus County Sheriff’s Department helicopter, flown by a deputy with a Modesto, Calif., police officer in the second seat, was on patrol in the Turlock area. It arrived six minutes after the first 911 call, said Deputy Royjindar Singh, the sheriff’s spokesman.

The helicopter landed in a nearby cow pasture and the Modesto police officer jumped out. He drew his service pistol and commanded the man to stop from about 10 feet away from behind a set of electric and barb wire fences. The officer yelled at the passersby to get out of the way. When the man “continued to stomp the child,” the officer fired, Singh said.