Police say Santos Navor-Flores shot and killed 21-year-old Manuel Campos in the 1600 block of 5th Street and South Union Avenue at about 12:30 a.m.
Authorities say Campos was outside an apartment building, drinking with some other people. Flores allegedly got angry that the group was there and they got into an argument.
Police say Flores went inside and got a gun, and then came out and fired several shots, hitting Campos in the head. He was pronounced dead at the scene.
"He died right there on the spot," said neighbor George Ponce. "I knew because their friends were trying to take him to a hospital but it was too late."
Authorities say the motive appears to be a dispute only and not gang related.
Flores is described as a male Hispanic, 5 feet 7 inches tall and 170 pounds. He also has dark and brown eyes.
If you have any information you're urged to call (877) LAPD-24-7 or (877) 527-3247.
City News Service contributed to this report.