A man who was fired from his job at a Southern California casino shot and killed a man in his former manager's office Tuesday, then fatally turned the gun on himself, authorities said.

Donnell Roberts, 38, walked into the Barona Gaming Commission building around 10 a.m. with a shotgun slung over his shoulder, ordered three secretaries to leave, then quickly opened fire in the manager's office, said San Diego County Sheriff Bill Gore.

Another 13 to 15 people fled through a back door, Gore said. Witnesses heard three shots.

The bodies were discovered about five hours later when authorities sent two robots to the office, Gore said. He declined to identify the victim until his family was notified.

"Our worst fears were confirmed," Gore told reporters outside the convention center of the Barona Resort and Casino. "It appears to be a murder-suicide."

Roberts, of El Cajon, Calif., was fired in November as an investigator with the commission and worked previously as a security guard for the casino.

San Diego County sheriff's deputies and California Highway Patrol officers surrounded the gaming commission building, located behind the casino.

Authorities never established contact with Roberts, Gore said.

The casino in the east San Diego suburb remained open throughout the ordeal but a parking garage and day-care center were closed, said Rick Salinas, the casino's general manager.

Salinas said he didn't know why Roberts was fired from the commission, which functions as the tribe's regulator of its casino. He was one of about three investigators and 30 to 40 employees working for the commission.

"He was a professional, he did his job, and from my understanding he did it well," Salinas said.

The general manager said he hugged several commission employees.

"They're all pretty shaken up," he said.

Gore said the employees he spoke with were "very distraught."

"It's been a very traumatic day for all of them, I'm sure," he said.

The resort, which includes a 400-room hotel, golf course and spa, is operated by the Barona Band of Mission Indians and employs about 3,000 people.

The tribe bought the reservation property in 1932 after its original reservation land was used to build a reservoir. Tribal gaming began there in 1994 with the opening of the Barona Casino Big Top.

The five-member gaming commission meets about three times a week, said Sheilla Alvarex, director of government affairs for the tribe.

Commission members are not all tribal members but they are employees of the tribal government, Salinas said.

"They are responsible for ensuring that the management team is complying with all regulations," she said.