The Los Angeles County Coroner's Office identified the shooter as 48-year-old Andre Turner of Norco.
According to police, Turner, a seven-year Edison employee, shot four of his co-workers with a semi-automatic handgun, killing two of them and wounding two others. Officials say Turner then turned the gun on himself and took his own life.
The two victims who were killed were identified as 53-year-old Robert Lindsay of Chino and 57-year-old Henry Serrano of Walnut.
Both were longtime employees and managers. Lindsay was with Edison for 29 years and Serrano was there for 26 years.
The two others injured - Angela Alvarez, 46, of Glendale, an Edison employee, and Abhay Pimpale, 38, of Montebello, an independent contractor - were hospitalized in critical condition. Pimpale was released from the hospital Saturday afternoon, but Alvarez was still in critical condition.
The shooting broke out about 1:30 p.m. Friday at Edison's No. 3 building in the 4900 block of Rivergrade Road.
People who knew Turner described him as a nice man. They said his house was up for short sale and he and his wife planned to buy another house.
"He seemed like a real stand-up guy," said Shane Tucker, Turner's realtor, adding that t. "I just don't see - me, personally, as a realtor - I don't see why short-selling the house would trigger anything negative, so it has to be something else."
Detectives are working to determine the motive behind the shooting. Authorities say they plan on searching Turner's home and looking at surveillance footage from inside the building at the time of the shooting.
Olive Junior High School and Walnut Elementary School in the Baldwin Park Unified School District were placed on lock down for some time following the shooting.
SWAT and emergency response teams surrounded the building as employees barricaded themselves inside conference and break rooms.
Many contacted family members using cellphones, and loved ones say they just tried to keep them calm.
"I was telling her, just do what she has to do to survive and be safe," said Ron Orona, whose daughter works in the building.
Monica Salazar said her mother, a 30-year Edison employee, was inside the building at the time of the shooting. Her mother communicated through text message, saying a group of them had locked themselves in a conference room.
As Salazar was being interviewed by Eyewitness News, she was reunited with her mother.
Edison is calling the shooting one of the worst days in the company's 125-year history. The utility will be offering funds and grief counseling for employees and the families of the victims.
Edison said employees at Irwindale are not required to show up to work Monday.