James A. Cervera, the police chief in Virginia Beach, said investigators were focused on establishing what Mr. Craddock’s motives were and whether his job status “had anything to do with the horrific acts and events that he perpetrated.”

At a news conference on Sunday, Chief Cervera offered a chilling timeline of what happened in Building No. 2, the stately 1970s-vintage brick structure where Mr. Craddock opened fire on three floors and where a small team of police officers rushed to confront an employee who had become an assailant.

The first urgent calls, the chief said, were received at 4:08 p.m., and less than two minutes later officers were outside the building, which over the years had become what he called a “honeycomb” of rooms and passageways. There was no time to consult a blueprint, no time to map out a strategy. They had to find the gunman.

By 4:18 p.m., the chief said, the officers had located Mr. Craddock, a 40-year-old former soldier who was armed with two handguns and plenty of ammunition.