A California doctor died after he was hit by a car while riding his bike and then stabbed by the driver, authorities said.

Dr. Michael J. Mammone, 58, was traveling along the Pacific Coast Highway in Dana Point around 3 p.m. on Feb. 1 when a driver struck him from behind, according to a press release from the Orange County Sheriff’s Office.

The driver, identified as Vanroy E. Smith, 39, then allegedly got out of his vehicle with a knife and began stabbing Mammone, a physician at Providence Mission Hospital in Laguna Beach.

Smith was also allegedly holding a BB gun when he approached Mammone. According to witnesses, he then assaulted Mammone in the intersection, where Mammone was found with “severe injuries,” per CBS News.

Bystanders were able to detain Smith before deputies arrived and arrested him, authorities said. Smith was booked into the Orange County Jail on suspicion of murder.

It is not immediately clear if Smith has entered a plea or retained an attorney to speak on his behalf.

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The knife he allegedly pulled out was also recovered at the scene, authorities said. It is unclear whether a gun was recovered.

Mammone was pronounced dead at a local hospital a short time later, according to the sheriff’s office.

Authorities have not discussed motive or whether the two men knew each other.

“Investigators are keeping all options open to check those boxes if you will, to make sure they don’t leave anything uncovered,” Orange County Sheriff’s Sgt. Mike Woodruff told KTLA.

Providence Mission Hospital issued a statement Thursday confirming Mammone’s death.

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

Dr. Dawn Aatwal, a cardiologist at the hospital, told Fox 11 that Mammone “saved so many lives here,” adding how the violence happened not far from where he worked.

“That’s the irony of this whole thing,” she said. “If a patient was brought in his condition he would have done everything he could to save that person.”

According to his profile on U.S. News and World Report, Mammone has more than two decades of medical experience.