A utility company office worker shot four colleagues on Friday with a semi-automatic handgun, fatally wounding two before killing himself in a business park outside Los Angeles, police said. \"As far as we know there was one shooting suspect, period,\" said Baldwin Park police Capt. Michael Taylor. The shooting around 1:30pm at Southern California Edison offices forced a lockdown of a large office complex and nearby schools as officers from surrounding cities and the Los Angeles County Sheriff Department\'s SWAT team responded. \"This is one of the most horrible days in our company\'s history,\" said Edison International Chairman and CEO Ted Craver. \"We are deeply saddened by today\'s tragic events.\" A man and a woman were wounded by gunfire and were listed in critical condition at local hospitals, said Sheriff\'s Lt. Holly Francisco. Three men were killed in the shooting - two bodies were found on the scene and a third died en route to a hospital. Four of the shooting victims were company employees and the fifth was a contract worker. Craver was careful not to provide identifying details for the victims, saying the company was still working to contact family members. There was no immediate word on what prompted the gunfire. Police could not confirm media reports that at least two of the targeted victims were believed to be company managers. No gunfire was exchanged after officers arrived. In the hours after the shooting, police cars, ambulances and fire trucks surrounded the building, and dozens of workers emerged with their hands over their heads. The complex is surrounded by a fence and patrolled by a security guard. Employees need a security card to get into the building, said Gil Alexander, a spokesman for Southern California Edison. About 230 employees work in the building where the shooting took place, and about 1,100 employees work in the complex. The utility\'s office is in a complex of buildings that also includes a business called California Lighting Sales. Cindy Gutierrez, the controller for that company, said employees there didn\'t hear gunshots and didn\'t realise anything was amiss until building management announced over the intercom that everyone should stay indoors. Two nearby schools were locked for about two hours after the shooting and no one on the campuses was hurt. Irwindale is a small industrial city of about 1,400 residents in the San Gabriel Valley, east of downtown Los Angeles. It is home to the Irwindale Speedway auto racetrack and large rock and gravel quarries. Southern California Edison is one of its largest companies, employing 2,100 people.