ORANGE, Calif. (AP) _ Highway authorities tightened security Friday at the maintenance yard where a man who blamed a supervisor for getting him fired walked in with an AK-47 and killed his former boss and three others.

The gunman, Arturo Reyes Torres, had claimed the supervisor he killed was in charge of an under-the-table recycling scheme that eventually led to Torres' dismissal six months ago, according to state personnel documents.

Police fatally shot Torres, 43, ending Thursday afternoon's bloodbath. A police officer and two other employees of the California Department of Transportation were wounded and expected to recover, officials said.

There have been 153 employee fatalities in a century of department operations, but this was the first fatal workplace shooting, said department spokesman Albert Miranda.

``He slipped through the gates undetected,'' Miranda said.

Torres, like other state employees terminated for cause, was told to stay away from state property, Miranda said, but up to 60 people were coming or going through the open gate as he began firing.

``They hid behind desks, they hid on the floor,'' he said.

Among those killed was Torres' former boss, maintenance supervisor Hal Bierlein, 51.

On Feb. 24, Bierlein and another supervisor videotaped Torres, an equipment driver, and his brother, James R. Torres, coming from a salvage yard where they had sold scrap aluminum from a bridge project, according to a state Personnel Board decision notice dated Sept. 29.

Bierlein, questioned by one of his bosses who noticed the low level in a scrap bin, had gathered his work crew Feb. 21 to read them regulations against pilfering.

The Torres brothers told the personnel board that Bierlein was actually in charge of this scheme. Several times, the brothers testified, they gave their boss receipts and $100-$200 in cash. They admitted selling state property, but said it was for crew social events, not for themselves.

An administrative judge said their story was ``persuasive.'' The brothers were fired anyway.

Concerned officials on Friday beefed up security here and at other department yards and offices, said Miranda. At the district's headquarters in neighboring Santa Ana, ID tags were required, side doors were locked and Highway Patrol officers were assigned to watch.

Complete security, Miranda acknowledged, would be next to impossible.

``How do you protect a yard that has to be open 24 hours a day?'' he said.

Torres had worked 12 years for the department.

Also killed in the shooting were Michael Kelley, 49; Paul White, 40; and Wayne Bowers, 43.