Goleta, Calif. ? A former postal worker who had been put on medical leave for psychological problems shot five people to death at a huge mail-processing center and then killed herself in what was believed to be the nation’s deadliest workplace shooting ever carried out by a woman.

The attack Monday night also was the biggest bloodbath at a U.S. postal installation since a massacre 20 years ago.

The rampage – the nation’s first deadly postal shooting in nearly eight years – sent employees running from the sprawling Southern California complex and prompted authorities to warn nearby residents to stay indoors during their initial search for the killer.

The 44-year-old woman, identified as Jennifer Sanmarco of Grants, N.M., had not worked at the plant for more than two years but still managed to get inside the fenced and guarded Santa Barbara Processing and Distribution Center. She drove through a gate by following closely behind another car, then got in the front door by taking an employee’s electronic identification badge at gunpoint, authorities said. The employee was not hurt, authorities said.

She opened fire with a 9 mm handgun, reloading at least once during the rampage, Santa Barbara County Sheriff Jim Anderson said.

Authorities found two people dead outside the plant, blocks from the University of California, Santa Barbara. Another body was just outside the door, and a wounded woman was just inside. Three more bodies – including that of the killer – were farther inside.

The wounded woman, Charlotte Colton, 44, was hospitalized in critical condition. She had been shot in the head.

Postal Inspector Randy DeGasperin said the woman had been placed on medical leave in 2003 for psychological reasons. He said she had been removed from the building by sheriff’s deputies that year for acting strangely. She made no threats, but other workers were afraid she might hurt herself, authorities said.

The dead were identified as Ze Fairchild, 37, Maleka Higgins, 28, Nicola Grant, 42, Guadalupe Swartz, 52, and Dexter Shannon, 57. All of the victims were thought to be postal center employees.