Investigators still searching for a motive in a deadly mass shooting that killed 12 people and injured four at the Virginia Beach Municipal Center in May are focusing on whether the city had created a hostile environment for its black employees. The attack was carried out by DeWayne Craddock, 40, a black city engineer who had submitted his resignation only to return fully armed to carry out the massacre on both and black and white co-workers. Arnette Heintze, CEO of a private security management firm consulting on the probe, said reports of a hostile work environment have become a key focus of an independent investigation into the shooting. “These issues included allegations that African American employees were being treated differently; that they were often more subject to discipline than their counterparts, that they were less likely to be promoted than their counterparts,” Heintze said as he delivered a preliminary report Tuesday evening in the same building where the shooting occurred. “That these employees felt that they could not share their concerns with management for fear of retaliation.”