Witnesses say there was some sort of altercation and shots were fired.
The guard was taken to a local hospital in critical condition, and he was declared dead a few hours later.
"I don't know how many times he was hit. We just know multiple shots were fired based upon witness statements," said Captain Denis Cremins, Los Angeles Police Department.
The security guard had worked at the Bank of America branch for a few years. He was hired by a private firm but contracted by Bank of America.
Eyewitness News learned the guard was armed. However, at this point in the investigation, it is unknown whether or not he fired back.
"Right now there are more questions than there are answers. We're canvassing the neighborhood and we've got an active investigation. We're bringing in a number of detectives to work the scene," said Deputy Chief Kenneth Gardner, Los Angeles Police Department.
The suspects are described as being young men in their late teens or early twenties.
Jimmy James banked here for years and considered the guard a friend.
"I'm feeling hurt, sad, kind of upset too. And, anger that they did that to him. He's a real nice guy. And I don't know if they were trying to rob the bank or what, but, they didn't get any money ... not a penny! Why would you want to kill a guy?" said James.
According to James, Thursday was to be the security guard's last day on the job.