OAKLAND, Calif. -- An Oakland man who was given a plea deal took the witness stand Wednesday, testifying against a member of the notorious "Nut Cases" gang about a 2003 killing spree that left two men dead in Oakland and another in San Francisco.

The 23-year-old man, who asked that his name not be disclosed, told jurors that he was with 25-year-old Monterrio Davis and several other men in what prosecutor Chris Lamiero said was "an evening of slaughter and mayhem" the night of Feb. 18, 2003, and the morning of Feb. 19, 2003.

The spree included two shooting incidents in Oakland and one in San Francisco as well as robberies and attempted robberies.

Davis is charged with three counts of murder and one count each of attempted robbery and being an ex-felon in possession of a gun.

He also faces two special circumstances clauses that could cause him to spend the rest of his life in prison without the possibility of parole if he's convicted: murder during a robbery and multiple murder.

The 23-year-old witness faced similar charges and a similar sentence but on June 14, 2005, prosecutors agreed to let him plead guilty to the lesser charges of two counts of voluntary manslaughter and other minor charges and receive a prison term of only 15 years and eight months in return for his testimony against Davis.

In his opening statement last week, Lamiero alleged that Davis was the shooter who "gunned down" 22-year-old Daniel Martinez and 47-year-old Miguel Maciel-Galena near the corner of 68th and Bancroft avenues about 8:45 p.m. on Feb. 18, 2003, while the two victims, who were day laborers, took a break from an English class.

Lamiero said Davis and three other men who were with him at the time robbed Martinez and Maciel-Galena so they would have enough money to fill up the gas tank of the car in which they were driving and smoking marijuana.

But the 23-year-old witness, who was dressed in a red jail jumpsuit, admitted Wednesday that he was the person who shot a 50-year-old janitor on 60th Avenue in Oakland at 12:15 a.m. on Feb. 19 when the man came home from his job at the Oakland Coliseum.

The janitor managed to survive and testified against Davis last week.

Lamiero alleges that Davis gave his gun to the 23-year-old witness and told the younger man to rob the janitor.

Lamiero also alleges Davis was the lookout in a third incident at 3:36 a.m. on Feb. 19, 2003, in which 26-year-old Armando Arce was shot to death by a third suspect on Willow Alley near Polk Street in San Francisco.

He said some of the culprits in the San Francisco incident were different than some of the participants in the Oakland crimes.