VIRGINIA BEACH, Va. (WAVY) — The city of Virginia Beach is continuing to heal one week after a dozen people were killed in a mass shooting.

A gunman opened fire at the city municipal center last Friday, killing 11 city employees and one contractor. Four others who were injured in the shooting remain hospitalized.

The lives of the victims were honored in a community gathering Thursday night at the Rock Church.

The shooting prompted city officials to close the offices at the municipal center the following Monday. City workers returned to complex on Tuesday as most of the city offices reopened.

Building 2 — where the shooting happened — has remained closed as authorities are working determine a motive for the shooting, which Mayor Bobby Dyer described as “‘the most devestating day in the history of Virginia Beach.”

Police said it took just 10 minutes or less from the time someone called 911 until police found the shooter inside the building.

Chief Jim Cervera says the building is a maze with three floors with many office Responding officers found the suspect on the second floor and engaged in a long gun battle.

Officer was hit during the exchange of gunfire, but was saved by his bulletproof vest. The shooter was shot and officers gave him first aid at the scene, but he later died at an area hospital.

Investigators with the FBI are working to track each bullet fired last Friday and recreate the scene at Building 2. The FBI said earlier this week the investigation could take seven to 10 days to complete.

FBI Special Agent in Charge Martin Culbreth said, “We’re looking where (the bullets) went to and what path they went along the way.”

The Associated Press reports police at one point were unable to confront the gunman because they didn’t have the key cards needed to open doors on the second floor of the building.

Officers were reportedly heard over scanners becoming exasperated as they tried to access locked areas.

“That’s definitely a blind spot that this particular shooting has shown,” said Gregory Shaffer, a retired FBI agent and former member of the bureau’s elite hostage rescue team.

City officials said the gunman was an engineer with the utilities department who was “in good standing” and showed “satisfactory” job performance. He submitted a resignation email the morning of the shooting.

The Office of the Chief Medical Examiner confirmed the gunman died of “multiple gunshot wounds sustained during an active shooter incident.” His manner of death is homicide, which means none of the gunshot wounds were self-inflicted.

Police identified the gunman as 40-year-old DeWayne Craddock, but chose to name him just once — choosing to focus instead on the victims.