The robbery unfolded around 2:05 a.m. in the 1400 block of Blue Jay Way, according to Los Angeles police.
Investigators say three suspects were in a car, and two of the men -- who were armed and wearing ski masks -- got out, forced two victims onto the ground and took watches and jewelry from them.
During the crime, police say an armed security guard exchanged gunfire with the suspects and was shot in the stomach. He was taken to a hospital in critical condition.
The two victims and the two robbers were also hit, according to police.
Sources within the LAPD tell Eyewitness News that they can confirm the security guard, a retired law enforcement officer, was working as personal security for Saghian, the CEO of the Instagram-driven fashion brand Fashion Nova.
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Following the shooting, the two wounded suspects got into their car and fled the area with the third suspect, police said. A description of the gray Audi was broadcast, and officers stopped it at Doheny Drive and Santa Monica Boulevard in West Hollywood.
One of the suspects was pronounced dead at that location, another was taken to an area hospital for treatment for a leg wound and the third was taken into custody.
LAPD said the two robbery victims were taken to a hospital in stable condition.
The victims were identified as men in their 40s, 50s and 60s.
Investigators say they found a gun in the getaway car and they do have surveillance video.
"We're not sure who the target was or what the motive behind this was other than property," said LAPD Detective Meghan Aguilar.
Detectives continue to investigate if the crime was an isolated incident or if it is connected to a rash of other robberies.
City News Service contributed to this report.