VIRGINIA BEACH, United States, June 1 (Xinhua) -- On Saturday morning, a local resident laid a bunch of white flowers under a tree on the pavement connecting Building No. 2 of the Virginia Beach Municipal Center. He wanted to express condolences.

"It could have been me. I could have been here. It could have been some of my loved ones," the resident, who did not want to give his name, told Xinhua.

Virginia Beach, a resort city in the southeastern U.S. state of Virginia, was plunged into grief on Saturday after 12 people were killed and four others were injured by a gunman who opened fire "indiscriminately" in a municipal building a day earlier.

The shooter was identified by police as 40-year-old DeWayne Craddock, once a city engineer at the city's public utility department for the past 15 years. He was employed at the time of the mass shooting and "authorized to enter the building," said City Manager Dave Hansen. U.S. media described the shooter as a "disgruntled employee."

Craddock died after a "long gunbattle" with four police officers and after roaming three floors and shooting at terrified people. He was said to have used two .45 caliber pistols equipped with a "sound suppressor" device and extended ammunition magazines.

Those guns were purchased legally, said investigators, adding that they have recovered more weapons from the gunman's house.

Virginia Beach police chief Jim Cervera declined to comment on any possible motive. "Right now, we have a lot of questions. The whys, they will come later. Right now, we have more questions than we have answers," Cervera said.

Vigils commemorating the victims were held in Virginia Beach throughout Saturday. "We are a heartbroken city," said Julie Hill, communications director for the city. "We lost 12 people who did nothing more than go to work."

U.S. President Donald Trump has ordered U.S. flags to be flown at half-staff in memory of the victims. He was ordering the action as a "mark of solemn respect for the victims of the terrible act of violence," according to the White House on Saturday.

"This is the most devastating day in the history of Virginia Beach," Mayor Bobby Dyer said Friday.

The Virginia Beach shooting was the worst mass shooting in the United States since November 2018 when a dozen people were killed at a California bar.

The Gun Violence Archive, a Washington-based not-for-profit corporation, has documented more than 150 mass shootings so far this year in the United States. Some 5,866 people were killed and 11,222 injured by gun-related incidents within the nation since Jan. 1, it said.

Eleven of the 12 victims killed in Friday's shooting were employees of the city. The other was a contractor seeking a permit.

"I have worked with most of them for many years," Hansen said. "They leave a void that we will never be able to fill."