The 37-year-old victim was shot once next to his white BMW. He was transported to an area hospital where he was pronounced dead. His name has not been released.
At least one suspect fled the scene. Detectives said they don't know if the shooter had an accomplice.
Detectives were continuing to investigate the shooting Wednesday, but did not have any suspect information. They said there are no signs of a robbery.
The victim was apparently shot after he stepped out of the office building to have a cigarette.
The incident has left co-workers and residents in Stevenson Ranch on edge.
"Somebody came running in and said he passed out, we all ran outside and just found him lying there," said co-worker Pete Adelson.
The victim, a father of three, owned a credit repair business. Employees said he opened the office in Stevenson Ranch a few months ago and business was good.
"He was such a nice guy. He was so friendly and open and polite to everyone, and to have something like this happen it's really, really tough," said Adelson.
Anyone with information about the shooting was urged to contact the Los Angeles County Sheriff's homicide bureau at (323) 890-5500.