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The shooter who opened fire indiscriminately in a Virginia Beach city building Friday afternoon, killing at least 12 people and sending six others to the hospital, was a disgruntled employee, a Virginia government source briefed on the investigation told CNN.

The shooter died after a gunfight with police.

Police Chief James Cervera told reporters Friday night the gunman was a public utility worker.

“This is the most devastating day in the history of Virginia Beach,” said Mayor Bobby Dyer. “The people involved are our friends, coworkers, neighbor, colleagues.”

Cervera said the shooter was confronted shortly after opening fire on multiple floors. There was an exchange of gunfire with officers, the chief said.

A police officer whose ballistic vest stopped a bullet was injured, the police chief said.

Edward Weeden, who works in the building, told CNN affiliate WAVY that people heard someone falling in a stairwell and went to investigate. He and his coworkers saw a woman who was down, blood all over her face.

One of Weeden’s coworkers went up to the next floor and came right back. “Get out of the building. The guy’s got a gun,” the woman said.

Weeden said he was unsure at first how to react.

“In a way you want to stay, in a way you don’t want to stay,” he said.

Gordon Rago, a reporter at The Virginian-Pilot, said witnesses described the scene as “frantic.”

He said the shooting occurred when people were still visiting the municipal center to conduct business.

Witnesses told him that SWAT officers were running down the street, directing them to get inside.

“I’ve talked to people who said that they were hiding under their desks,” Rago said.

Police found a pistol and a rifle at the scene that investigators believe were used in the shooting, according to a law enforcement official.

The suspect is thought to have purchased the firearms legally, according to initial information that investigators have, the source says.

Virginia Beach Vice Mayor James Wood said people can take guns into public buildings, but not schools or courts.

The mass shooting took place in Building 2 of the municipal center, according to police.

Building 2 of the Virginia Beach Municipal Center houses the operations building for the city, which include multiple departments.

Six people were hospitalized after the shooting, hospital officials tweeted.

Virginia Beach General Hospital said there were five patients there. A patient who was at Princess Anne Hospital was being transferred to Norfolk General Hospital, a Level I trauma center.

The FBI is also responding to the incident to provide assistance to local authorities, an FBI spokeswoman told CNN.

The incident is the deadliest mass shooting in the US since November.

In that shooting, 12 people were killed at the Borderline Bar & Grill in Thousand Oaks, California. Officials said that gunman, Ian David Long, shot an unarmed security guard outside the bar, went in and continued shooting, injuring other security workers, employees and patrons. Long died by suicide.

Virginia Sen. Tim Kaine tweeted that he was devastated by the news Friday.

“My heart is with everyone who lost a loved one, and I’m praying for a swift recovery for all those who have been injured,” he said.

Sen. Mark Warner wrote: “Praying for all involved as we learn more.”

“We are praying for our city, the lives that were lost, their families and everyone affected,” singer Pharell Williams, who grew up in Virginia Beach, tweeted. “We are resilient. We will not only get through this but we’ll come out of this stronger than before we always do.”

President Trump has been briefed on the shooting, a White House spokesman Hogan Gidley said.

By Steve Almasy and Rebekah Riess, CNN