Editor’s Note: This account of the mass shooting at the Virginia Beach Municipal Center is based on official statements from city officials, police reports, and other reporting from CNN and its news affiliates.

CNN  — 

DeWayne Craddock, a 15-year public works employee, stopped in the men’s bathroom to brush his teeth near the end of his shift, like he did every day. But by late afternoon, instead of going home, he plotted to carry out a massacre.

A coworker asked if he had any weekend plans. Craddock said no, and they wished each other well.

City employees were still working at their desks at the sprawling campus of government offices in Virginia Beach around 4 p.m. on Friday. Residents were paying water bills and filling out permits.

Then suddenly, gunshots. First outside, then inside.

Craddock shot one person in the parking lot outside the Municipal Center and made his way toward the conference rooms and offices that were accessible only to employees with a key card.

Inside, the 40-year-old shot indiscriminately at victims on three floors, a sound suppressor muffling the gunfire.

People rushed to nearby buildings, stacked desks against office doors and hid in closets. The sound of screams rang in their ears. Some held hands in silence or sent desperate text messages to loved ones.

A woman was sitting in her car waiting for her daughter when she spotted a man with a bloodied shirt outside the building.

The gunman, who had submitted his letter of resignation hours earlier, killed 12 people – a contractor and 11 city workers, authorities said. Craddock died after a gun battle with officers. It was the deadliest massacre in the country this year.

“The victims are people we’ve worked with, people we know. They’re our friends. It’s just really, truly horrible,” Virginia Beach Vice Mayor James Wood said.

‘You could hear him walking around’

Some witnesses said they were unsure the muffled sounds they noticed from afar were indeed gunshots.

From a first floor office in Building 2, Zand Bakhtiari heard screams in the parking lot. Bakhtiari’s boss called and warned him there was a gunman in the building.

“I mainly texted my loved ones, and a couple of minutes after that I just heard rapid gunfire,” he said.

06:14 - Source: CNN
Witness: People were screaming to get down

Mike, an engineer, said he and his colleagues heard a woman scream. It was coming from a corner of the second floor where the engineering supervisors sat, including two of his bosses: Katherine A. Nixon and Richard H. Nettleton. Both were killed.

“We all started going toward the scream. And then we heard gun shots,” said Mike, who would only provide his first name.

He locked himself in his office and hid under his desk.

“He was shooting quickly. It wasn’t one shot, it was three shots, three shots,” Mike said.

“You could hear him walking around,” he said. “When the gunshot sounded far away, you knew he wasn’t there, but then he would come back.”

Gunshots, screams and chaos

Megan Banton heard the gunshots, yelling and screaming as she hid in her boss’s office with 20 of her coworkers.

“I have an 11-month-old baby at home, and all I could think about was him and trying to make it home to him,” said Banton, an employee with the city’s public utilities office.

Craddock’s coworker, Ned Carlstrom, said he heard shots and people screaming that there was a shooter in the building. But it didn’t sound real; he and his coworkers thought it was a drill.

City workers and residents gathered outside the city's municipal building to pay tribute to the victims.

Carlstrom said he passed by Craddock during the shooting as they walked out of the building.

“We passed by a gentleman that was carrying a gun in his hand, but it looked so theatrical because of the extended magazine and the suppressor that was on the end of it,” Carlstrom said. “He glanced at me, but he never raised the gun at me to shoot me.”

He later found out that Craddock was the gunman.

“I thought he was playing the part of an active shooter for our drill,” Carlstrom said.

Officers scramble

Around 4:08 p.m., officers were dispatched to the scene, said Virginia Beach police chief James Cervera.

Four officers were the first to respond to the scene, Virginia Beach Police Chief James Cervera said.

Two Virginia Beach police detectives at the station in the municipal complex heard calls on the scanner, immediately grabbed the bullet proof vests slung over their office chairs and ran about 300 yards to the scene.

They arrived first, along with two officers in the canine unit who had been patrolling nearby, a law enforcement source told CNN.

For five to eight minutes, the officers ran down the numerous hallways and stairwells of the more than 40-year-old building. They feared the shooter could be among those running out of the building.

Then they found the gunman on the second floor.

The officers exchanged gunfire with Craddock, killing him.

‘They leave a void’

After the shooting, officers looked for survivors in rooms and closets and under desks. They found victims scattered through building’s three floors. Some employees had to step over the bodies of slain coworkers when they were evacuated. One survivor recalled walking down a blood-stained stairwell.

The morning after the shooting, city officials stood in front of reporters reciting the names of the 12 victims and their titles. The tribute took nearly three minutes.

Herbert “Bert” Snelling, a local contractor, had come to the Municipal Center to file a permit when he was killed. The 11 other victims were engineers, account clerks, administrative assistants and right-of-way agents.

Tara Welch Gallagher, Mary Louise Gayle, Alexander Mikhail Gusev, Ryan Keith Cox, Joshua O. Hardy and Michelle “Missy” Langer of Virginia Beach were killed.

Chesapeake residents Laquita C. Brown and Robert “Bobby” Williams, who was a 41-year veteran of the public utilities department, also died in the shooting.

Christopher Kelly Rapp, who recently moved to Virginia Beach, had only been working as an engineer in the public works department for 11 months.

“They leave a void that we will never be able to fill,” said Virginia Beach City Manager Dave Hansen.

Tears and prayers

Over the weekend, people attended prayers and vigils in Virginia Beach to remember the victims. Some held hands and prayed in the parking lot of a movie theater in the morning rain.

People around Virginia Beach organized prayers and vigils Saturday to honor the 12 victims of the shooting.

Community members left flowers and other tributes next to the yellow crime scene tape that stretched around the building. A man arrived with 12 American flags and placed them in the ground.

Mike and Vanda Snyder, members of the nearby United Methodist Church, stood in silence and looked at the building from afar. After paying their respects, the couple brought chips and cookies for the law enforcement officers who were still working around the clock.

“There’s nothing we can do. You just feel helpless,” said Vanda Snyder, a retired nurse who worked in a nearby hospital emergency room delivering babies. “You want to do something. There’s nothing you could do.”

CNN’s Deanna Hackney, Steve Almasy, Amir Vera, Hollie Silverman, David Shortell, Mark Morales and Shimon Prokupecz contributed to this report.