The incident occurred in the 1200 block of West Union Street around 3 a.m.
Authorities say two beating victims with severe trauma arrived at Arrowhead Regional Medical Center.
One of the victims, later identified as a 39-year-old man, died of his injures around 12:15 p.m. Officials say the second victim, a 20-year-old man, was treated and released.
During the later investigation, police learned one of the suspects who assaulted the men was the deceased victim's coworker.
Gerald Gonzales, 20, of Highland was located on Union Street and arrested without incident.
Police are searching for additional suspects.
The investigation remains ongoing. Anyone with information was urged to contact Detective Bill Flesher at (909) 384-5655 or Sgt. Gary Robertson at (909) 841-5361.