Investigators have not yet been able to confirm whether any money or property was taken from the restaurant or from the nightshift employee who was killed, said San Mateo police Lt. Mike Brunicardi.
A daytime restaurant manager arrived at the eatery, located at 3101 S. El Camino Real, at around 5:15 a.m. today and found Douglas Castillo, 36, of Hayward, dead on the floor.
The manager immediately called police, who arrived within minutes. Castillo was pronounced dead at the scene.
Police began investigating Castillo's death as a homicide after noticing trauma to his head, Brunicardi said.
The death is the city's first homicide since 2006.
Details of the crime scene, such as where the body was found, are being withheld during the ongoing investigation.
Police have "pulled out all the stops" to investigate the incident, according to Brunicardi.
"This is a very high priority," he said.
T.G.I. Friday's Worldwide has announced a $10,000 reward for information leading to the arrest and conviction of the person or persons responsible for the worker's death, Brunicardi said.
A message from the restaurant's corporate officials was sent to police this afternoon announcing the reward and offering condolences to the victim's family.
"This is an absolute tragedy and our hearts and prayers go out to the family," the statement read.
T.G.I. Friday's is located across the street from Hillsdale Mall and is situated along the Caltrain tracks.