The incident was reported just after 12 p.m. near the 9100 block of Las Tunas Drive.
According to the Los Angeles County Sheriff's Department, the home is an illegal gambling establishment.
The man, described only as a Hispanic male, was found with at least one gunshot wound to his upper torso, investigators said. He was treated at the scene, but was later pronounced dead.
According to investigators, the 25-year-old was shot and killed after some sort of dispute. Neighbors said in the last month and a half, a suspicious crowd began coming around the building.
The property manager told ABC7 the building was leased to a security company.
"We just knew something was going on there for several months," said Pat Lacap, a Temple City resident. "It used to be a restaurant and got sold about five years ago, and we just always notice people in and out. We were always a little nervous, like, you know, hopefully nothing bad happened ... and something bad has happened."
The victim's name has not yet released and no motive or suspect description was provided.
Anyone with information is urged to contact the LASD Homicide Bureau at 323-890-5500.