Investigators in Orange County are still trying to determine why a driver struck a bicyclist with his car and then stabbed him to death in Dana Point on Wednesday.

The victim has been identified as Michael Mammone, 58, an emergency room doctor at Providence Mission Hospital in Laguna Beach.

Authorities say Vanroy Smith, 39, of Long Beach, struck Mammone with his white Lexus sedan at the intersection of Pacific Coast Highway and Crown Valley Parkway around 3 p.m. Wednesday.

Witnesses told deputies that after the collision, Smith got out of his vehicle and assaulted Mammone, stabbing him several times.

Smith was detained by witnesses at the scene until law enforcement arrived, authorities said.

Mammone died at a hospital.

Investigators have not yet found any connection between the two men.

“As of right now we currently don’t truly understand the why… as far as motivation and any type of relationship,” Orange County Sheriff’s Sgt. Mike Woodroof told KTLA. “Investigators are keeping all options open to check those boxes if you will, to make sure they don’t leave anything uncovered.”

Providence Mission Hospital issued a statement Thursday calling Dr. Mammone’s death a “stunning tragedy.”

“The entire Mission Hospital family is grieving over the loss of an incredible physician and friend,” the statement read. “We will honor Dr. Mammone’s dedication to our community and passion for medicine by continuing to provide exceptional care.”

Smith has been booked on suspicion of murder.