Authorities have yet to find what motivated a 48-year-old employee at a Southern California Edison utility office east of Los Angeles to shoot four people, ABC News is reporting. The employee, Andre Turner, shot his co-workers with a semiautomatic handgun on December 16, 2011, before turning the gun on himself. The shooting occurred in a complex that houses more than a thousand employees.

Utility spokesman Steven Conroy confirmed that Turner worked at Edison for seven years before the shooting. Two of Turner’s co-workers, Henry Serrano and Robert Scott Lindsay, both long-time information technology managers, were ultimately killed from their wounds. The Sheriff’s Department confirmed that the two other victims, Angela Alvarez and Abhay Pimpale, were taken to hospitals in critical condition. Pimpale was released the following day, but there’s no word yet on Alvarez’s condition.

All five involved in the shooting worked at the same building at the Irwindale office park. Authorities are still searching for the reason why Turner opened fired towards his co-workers, during which employees barricaded themselves behind locked doors and under desks. The office complex and nearby schools were locked down after the Sheriff Department’s SWAT team responded. Edison has called the shooting “one of the most horrific events the company has experienced in its 125-year history.”

Written by: Karen Benardello