LOS ANGELES (AP) — Some employees returned Tuesday to a Southern California Edison office, just days after a reprimanded worker shot and killed two supervisors and wounded two others before turning the gun on himself.

The Irwindale office east of Los Angeles reopened after the scene of rampage was investigated and cleaned up, but it was unclear how many of the 1,050 staff members went back to work, Edison spokesman David Song said.

Grief counselors were available for those who did.

"You really can't imagine what it's like to go through something like this," he said. "The feeling of unbelief, and obviously sadness and sorrow. It's a big company but in a lot of ways it's ... tight-knit. A lot of people are only one person removed" from a victim.

Security had been increased at the office complex.

Investigators said they were still trying to determine what sparked Friday's shooting by Andre Turner. He had been verbally reprimanded for missing an audit deadline but it was unclear exactly when that occurred, sheriff's Lt. Holly Francisco said.

The Press-Enterprise of Riverside has reported that Turner, 48, bought a 5,000 square-foot, five-bedroom house near Hidden Valley Golf Club for $711,000 when it was new in 2004 but was selling it for $590,000.

The leased office complex in Irwindale houses Edison's information technology department, where Turner and the victims worked, along with electrical transmission and distribution staff.

Turner, armed with a semiautomatic handgun, killed managers Robert Scott Lindsay, 53, of Chino Hills and Henry Serrano, 56, of Walnut, authorities said.

Angela Alvarez, 46, of Glendale, an Edison employee, and Abhay Pimpale, 38, of Montebello, a contract worker, were wounded.

Pimpale, the father of a 3-year-old son and a newborn baby, was released Saturday from a hospital.

Alvarez was upgraded from critical to serious condition at County-USC Hospital on Monday, spokeswoman Rosa Saca said.

In a 911 call released by authorities Monday, the operator says she heard possible gunfire while the security guard from the office park called to report the shooting.

"I heard a male voice in the background yelling," the operator said. "There's also some loud popping noises in the background."

Turner, a systems analyst, had worked at the company for seven years.

Lindsay was a manager in the IT division at Edison and worked for the company for 29 years, company officials said. He was married and was a father. Serrano, a manager in the same area, was with the company for 26 years.

Copyright 2011 The Associated Press.