A driver was arrested for allegedly running into a bicyclist and then fatally stabbing him on a Southern California roadway, authorities said.

Vanroy Evan Smith, 39, of Long Beach was taken into custody Wednesday on suspicion of murder for the attack Wednesday in Dana Point.

He remained jailed without bail on Thursday. It wasn’t immediately clear whether he had an attorney to speak on his behalf.

Michael John Mammone, 58, was in a bike lane on the Pacific Coast Highway at around 3 p.m. when he was struck from behind by a Lexus sedan in an intersection, according to the Orange County Sheriff’s Department.

The collision “launched him into the intersection,” sheriff’s Sgt. Mike Woodroof told KNBC-TV. “At that point, the suspect drove around the victim, exited his vehicle, went back to the victim and continued to assault the victim.”

The driver stabbed Mammone, who was pronounced dead at a hospital, a Sheriff’s Department statement said Thursday.

Bystanders held Smith for sheriff’s deputies. He was arrested and a knife was seized, authorities said.

Smith didn’t have any known connection to Mammone and investigators were still trying to determine a motive for the killing, authorities said.

Mammone was an emergency room doctor at Providence Mission Hospital in Laguna Beach.

His death is a “stunning tragedy,” the hospital said in a statement Thursday.

“The entire Mission Hospital family is grieving over the loss of an incredible physician and friend,” the statement read.