TURLOCK, Calif. - Police on Monday identified a man who was fatally shot by an officer for allegedly refusing to stop beating a toddler to death along a remote road.

Sergio Casian Aguilar, 27, parked his truck on an unlit road Saturday night, removed a 2-year-old boy from his car seat and proceeded to stomp, kick and punch the boy to death, authorities said. The boy was unrecognizable when he was pronounced dead at Emanuel Medical Center, the Stanislaus County Sheriff's Department said.

Authorities have not released the boy's name but say they believe he was Aguilar's son. The Stanislaus County coroner and the California Department of Justice are testing DNA to confirm the relationship.

Several motorists called 911 and tried to stop the beating, authorities said.

Dan Robinson, a local volunteer fire department chief, told The Modesto Bee that at first glance, he thought the child was a dead animal in the road. He said when he realized it was a child, he tried to stop Aguilar.

He said Aguilar had a "total hollowness in his eyes" and talked calmly of the boy being filled with "demons."

Witness Lisa Mota told the San Francisco Chronicle that Aguilar told people who tried to stop him that the boy was "trash."

Responding to 911 calls, a Stanislaus County Sheriff's Department helicopter landed in a dairy pasture near the scene. A Modesto police officer, Jerry Ramar, fatally shot Aguilar after he failed to heed the officer's warning to stop beating the child, authorities said. Aguilar flashed his middle finger at Ramar before Ramar shot him in the forehead, police said.

"I have never seen anything like that before and I hope I never have to again," Ramar said of the beating.

Authorities have not released the name of the boy's mother.

Aguilar had no previous criminal history, police said. Results of toxicology tests on Aguilar are expected in four weeks.

Ramar has been placed on paid administrative leave, a routine response for officer-involved shootings.