Police said the family became concerned when the victim, 47-year-old Hector Urias, didn't return home from work Tuesday night. They went looking for him and found him dead at the business he owned for two decades.
The discovery of Urias' body was originally called in as a possible suicide, but a preliminary investigation led authorities to believe that there might have been foul play.
"This is a murder investigation," said Lt. Don Slawson of the Los Angeles County Sheriff's Department. "There's evidence to indicate that this was not a suicide."
Urias was a well-known racer at Toyota Speedway at Irwindale.
"My brother was a good guy in this community and did a lot for it," said Urias' brother, Ramon. "Everyone is devastated by this. I don't know what to say. I'm at a loss for words."
Some family members said they can't imagine anyone wanting Urias dead.
"I don't know anyone who would want to hurt him," said his cousin, Johnny Urias. "I know many people who would have wanted to help him if he ever needed him. He was that great of a person. We're mind boggled. I'm totally shocked."
Detectives said Urias was shot at least once. They were unable to say what time he was killed, but said he did not show up to a league basketball game in El Monte about 9 p.m.
Family members became concerned when he didn't show up at all Tuesday night.
"Everybody knows him," Ramon Urias said. "Hopefully all his friends and everybody can come out and talk to their friends and find out who did this. That's all we want. Justice."
Anyone with information is asked to call sheriff's homicide detectives at (323) 890-5500.