SAN DIEGO -- A former Barona Gaming Commission staffer who opened fire Tuesday at the East County offices of the agency died at the scene, along with a gaming commission manager, in what authorities described as an apparent murder-suicide.

The assailant, identified as 38-year-old Donnell Roberts of El Cajon, entered a personnel trailer at the Lakeside-area office complex with a shotgun shortly before 10 a.m., told several receptionists to leave, walked into an adjacent manager's office and began shooting, Sheriff Bill Gore said.

The manager has been identified by authorities as 43-year-old Raymundo Casillas.

Witnesses reported hearing three shots.

"Shortly after all the employees evacuated, and we knew there were two people left in the building, the shooter and the victim, we ... set up a perimeter," Gore said. "And then we called in our SWAT teams ... And once that was done ... we tried to establish communications with whoever was inside, to no avail."

Shane Richardson of Detroit, a patron at next-door Barona Casino & Resort, told 10News that security personnel roped off the entrances and exits to the gambling hall following the gunfire and provided guests with little information. Otherwise, nothing seemed amiss inside the Lakeside-area tourist attraction, he said.

"Nobody really seems (to know) what's going on. ... It looks like normal," he said in the late morning. "Like, I've been in, coming in and eating and stuff, and it looks normal."

About 2:30 p.m., deputies sent a camera-equipped remote-control device into the office complex and determined that two people were inside, apparently dead, Gore said. Sheriff's personnel then entered the trailer and confirmed the deaths of Roberts and Casillas.

Roberts was a one-time Barona Casino security guard who held a white-collar post on the staff of the gaming commission until last month, when he resigned for undisclosed reasons, according to the commission.

Roberts' wife left him after he left his job, according to one local media outlet citing anonymous sources employed by the commission.