The robbery was reported at about 6:30 p.m. at a home in the 2300 block of Wayne Street, police said.
The victim said that a man knocked on his door, and after the victim opened it, the suspect displayed a handgun and was wearing a police badge on his waist, according to police.
The man, along with two other suspects, entered the home and tied up the victim and his friend before stealing jewelry and a vehicle from the home and fleeing.
The stolen vehicle was later found unoccupied in Pittsburg, police said.
No shots were fired in the incident, and no one was injured.
The victims were able to eventually free themselves from being tied up after about 30 minutes and contacted police.
Martinez police are investigating the incident, and any questions or witness information can be directed to Detective Sgt. Jon Sylvia at (925) 372-3450.
