Police received a 911 call reporting a shooting at 974 Triangle Circle in the Triangle Court public housing development just before 4:30 p.m., Gagan said.
Investigators believe there was a dispute over a drug transaction that led to the shooting of a resident, 26-year-old Michael Anderson.
Other people then reportedly shot and killed 19-year-old Oakland resident Dante Deloney and 28-year-old San Leandro resident Corey Walker II, Gagan said.
Two people were taken to the police station for questioning afterward but have since been released.
"After looking at the physical evidence and the statements they made, they are not being charged at this time," Gagan said.
Police declined to release further details about the shooting, citing the ongoing investigation.