It happened just before 9:30 p.m. at an apartment near 2008 Griffin Avenue near Darwin Avenue.
At the scene, responding officers found the victim, later identified as Jose Mancia, inside suffering from blunt force trauma. Mancia was pronounced dead at the scene.
According to the LAPD, Mancia was outside watching fireworks with his wife when the suspect entered the apartment. At some point, the victim went inside and encountered the suspect. Neighbors told police they heard an argument between the two people.
Mancia's wife was not physically injured in Monday night's deadly incident.
The suspect is described as a man wearing a mask and dark clothing.
A motive has not been established at this time.
The investigation remains ongoing.
Anyone with information is asked to call police.