Man trying to steal Freightliner tree-trimming truck at knifepoint dies after driver fights back, California sheriff says

California police are investigating an alleged armed carjacking attempt that turned fatal when the driver of a Freightliner work truck fought back against the attacker.

The incident occurred on July 18, 2026, in San Marcos, California, according to the San Diego County Sheriff’s Office (SDCSO).

Police responded to the 200 block of S. Pacific Street in San Marcos. Upon arrival, they found an adult male in the roadway suffering from severe head trauma. The man was transported to a local hospital.

The driver of a Freightliner tree-trimming truck told police that the injured man attempted to steal the truck while it was in motion.

The man, later identified as 56‑year‑old Mark Douglas Heninger, jumped on the truck’s running board armed with a knife, the driver said.

The driver and Heninger became involved in a physical fight. Heninger fell from the truck into the roadway.

The driver of the tree-trimming truck suffered minor injuries. He immediately called 911, stayed at the scene, and cooperated with police.

Heninger died in the hospital on July 20.

The investigation was taken over by Homicide Detectives.

“The circumstances and motive surrounding the incident remain under investigation,” SDCSO said.

If you have information, you’re asked to call the Homicide Unit at (858) 285-6330/after hours at (858) 868-3200.