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A Southern California man has pleaded not guilty to murder in the death of an off-duty firefighter hit by a car while bicycling in November.

Twenty-five-year-old Stephen Scarpa pleaded not guilty Friday in the death of Costa Mesa fire Capt. Mike Kreza, who succumbed to his injuries two days after he was hit in Mission Viejo.

Orange County prosecutors say Scarpa is suspected of driving under the influence of multiple controlled substances when he crossed into a bike lane, onto the sidewalk and hit Kreza.

In a separate case, an O.C. doctor is facing federal drug trafficking charges for allegedly selling Scarpa the powerful narcotics he was believed to be under the influence of at the time of the crash.

Dr. Dzung Ahn Pham, 57, is also linked to Ian David Long, the gunman who killed 12 people in the Borderline Bar & Grill mass shooting in Thousand Oaks. Long was found to be in possession of medication Pham had prescribed someone else, officials said.

Scarpa could face life in prison if convicted. He’s being held on $2 million bail.

The 44-year-old Kreza was married with three daughters.

KTLA’s Erika Martin contributed to this report.