MARTINEZ -- The slaying of one homeless man by another in Concord last week was motivated by a fight over a missing syringe of methamphetamine, Contra Costa County's head homicide prosecutor said Tuesday.

James Riley, 38, was arraigned in a Martinez courtroom Monday on charges of murder and assault with a knife in connection with the strangulation killing of 47-year-old Jerald Nagle. Riley, who is being jailed in lieu of $1 million bail, returns to court Dec. 20 to enter a plea to the charges.

Riley and Nagle and their girlfriends were outside a homeless encampment near Concord Avenue and Interstate 680 on Dec. 5 when Nagle was accused of stealing the drugs of Riley's girlfriend, deputy district attorney Mary Knox said.

Riley followed Nagle into the camp and attacked him with a knife before strangling him from behind with what he told investigators was a "Judo hold," Knox said.

Contact Malaika Fraley at 925-234-1684. Follow her at Twitter.com/malaikafraley.