SAN DIEGO -- A motorist accused of deliberately driving over a bicyclist, who was dragged more than 500 feet, pleaded not guilty Wednesday to murder and assault charges.

Marcos Garcia Jeronimo, 22, was ordered held on $1 million bail.

Deputy District Attorney Patrick Ojeil told Judge David Szumowski that Jeronimo and the victim, a young man believed to be a Mexican national, knew each other through a mutual friend.

"We're not sure of the motive yet, it's still part of an ongoing investigation," the prosecutor said outside court.

The defendant's Dodge Neon was stopped on a street within a sprawling apartment complex in Mira Mesa -- the bicyclist was in front of the car -- when the motorist allegedly drove over the victim about 3:45 p.m. on Aug. 20.

The bicyclist was dragged nearly 500 feet along the 8400 block of Capricorn Way and died at the scene. Authorities have not been able to positively identify him thus far.

Jeronimo fled the scene on foot but surrendered to Oceanside police last Saturday, Ojeil said.

The prosecutor said the suspect's brother, 20-year-old Alvaro Garcia Jeronimo, is charged with being an accessory to a crime.

The defendant -- who has an immigration hold placed on him -- faces 26 years to life in prison if convicted, Ojeil said.

He will be back in court Tuesday for a status conference and Sept. 10 for a preliminary hearing.