According to police, the gunman, a driver, pulled over the company bus on Tuesday in western Cairo, whipped out an assault rifle and showered his passengers with bullets.
The official spoke on condition of anonymity because he is not authorized to speak to the media.
The Arab Contractors company identified the assailant as 53-year-old Mahmoud Sweilam, in a statement issued after the attack. It said he had hidden his weapon under the bus seat and then turned himself in after the shooting, which took place just 300 meters from company premises.
Effat Abdullah, the company spokesman, said that Sweilam spent 20 years in the company, one of the largest construction companies in Egypt, but declined to comment on a possible motive for the attack.
According to the security official, the gunman appeared to have suffered severe depression after he was transferred to a new position.
The incident was a rare case of workplace violence in Egypt, which experienced some terrorist attacks in the 1990s as well as occasional inter-family vendettas in the impoverished south.
