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Staffers who worked with a Southern California emergency room physician authorities say was killed by a motorist in a bizarre attack while on an afternoon bicycle ride called him an "amazing doctor."

Co-workers at Providence Mission Hospital Laguna Beach told FOX Los Angeles that Dr. Michael Mammone would often bike to work because he lived just blocks from the facility. 

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"That's the irony of this whole thing. If a patient was brought in his condition he would have done everything he could to save that person. He has saved so many lives here, and he died very close to where he saved hundreds of lives," said cardiologist Dr. Dawn Aatwal.

Orange County doctor killed

Dr. Michael Mammone, 58, was killed Wednesday by a motorist who struck his bicycle and then attacked him in Southern California, authorities said.  (Providence Mission Hospital Laguna Beach)

Mammone was killed Wednesday as he was bicycling on Pacific Coast Highway in the coastal city of Dana Point. A motorist in a Lexus struck from behind and then got out of the car and assaulted Mammone, 58, with a knife, authorities said. 

Witnesses said the suspect, identified as Vanroy Evan Smith, 39, was detained by bystanders. He was arrested on suspicion of murder. A knife believed to have been used in the attack was recovered. Investigators said there doesn't appear to be a connection between Mammone and Smith. 

Mammone has worked at the hospital since 2011. In a previous statement to Fox News Digital, the hospital said it was "stunned by this devastating tragedy."

California suspected killer of doctor

Vanroy Smith is accused of killing Dr. Michael Mammone this week.  (Orange County District Attorney's Office)

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

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Smith appeared in court Friday where he pleaded not guilty to murder and an enhancement of the personal use of a knife. He faces up to 25 years to life in prison. 

"An innocent man is dead because he took a bike ride to enjoy a beautiful California day along the beach and he was hit with a car and stabbed to death by someone he apparently never met," Orange County District Attorney Todd Spitzer said. "The murder of a complete stranger in broad daylight for what appears to be absolutely no reason is the stuff of nightmares. This unspeakable act of violence will forever haunt those who were forced to witness it and it will forever haunt all of those who loved Dr. Mammone."

Smith is being held on $1 million bail and expected to appear in court on Feb. 14.