The $20,000 reward was announced Tuesday by Los Angeles County Supervisors Mike Antonovich and the Arcadia Police Department.
Part of the crime was captured on surveillance tape. On the tape, the suspect can be seen entering through the restaurant's backdoor just before 9:30 p.m. on November 25, and confronting three employees.
"As he was moving those individuals to the front of the restaurant, for whatever reason, he fired a shot that struck Mr. Wei," said Arcadia Police Lt. Ron Buckholtz.
Police are unsure why the suspect fired his weapon, and there was no sign of resistance during the robbery.
The shooting itself was not caught on tape, but the suspect was seen moments after shooting walking toward the front door of the restaurant, then returning to the cash register to demand money.
He took $200 dollars and left.
Anyone with information is asked to call Arcadia Police Department at (626) 574-5150.