VIRGINIA BEACH, Va. – The longtime Virginia Beach public works employee accused of the nation's latest mass shooting put in his two-weeks notice Friday morning, hours before the attack that killed 12 and wounded four, city officials said Sunday.

Virginia Beach City Manager Dave Hansen said DeWayne Craddock's job performance was "satisfactory," he did not face any disciplinary measures before he notified the city that he intended to quit, and he was not fired.

"He was in good standing within his department, no issue of discipline ongoing," Hansen said.

In an interview with USA TODAY, Virginia Beach Police Chief Jim Cervera said the gunman’s motive is a mystery to authorities – a glaring question that may never be answered. Craddock died after the shooting.

“Right now, we’re open to everything on his motive. We haven’t focused in on any one thing,” he said. “You have a professional life, you have a personal life. Is it something that happened in his personal life? Is it something long-term that happened in his personal life?”

Cervera said investigators are looking at everything from his electronic trail and finances to his resignation and relationship with co-workers. He said nothing has stuck out that could explain why the gunman snapped.

Authorities worked to put all the pieces together and track the shooter’s exact movements Friday to see whether there were any signs, but Cervera said, “Anecdotally, what I’m hearing is it was a regular workday.”

Four shooting victims all had multiple operations and were recovering Sunday at two area hospitals. One at Sentara Virginia Beach General Hospital was downgraded from fair to critical condition after a surgery, and two others there remained in critical condition.

A fourth victim was critical but stable at Sentara Norfolk General Hospital, which handles higher-level trauma cases.

Sunday, residents of this resort town about 200 miles south of Washington flocked to churches as they grappled with the horrific incident.

At Lifehouse Virginia Beach, Pastor Brandon Shank's praise for the police response received rounds of applause. He assured congregants the rampage would not define the Virginia Beach community and issued a call for unity. “What took place in this city is not who we are,” Shank said.

Craddock was described by police and those who knew him as an enigma who gave no indication that he stockpiled an arsenal and planned a systematic assault on his colleagues.

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Craddock, a 15-year veteran of public works and a civil engineer, was still employed at the time of the rampage and had a pass to enter the secure inner offices and conference rooms.

Police arrived two minutes after emergency calls about shots fired at Virginia Beach's municipal building No. 2 at 4:08 p.m., Cervera said Sunday.

He described the three-story municipal building with a basement as a "honeycomb," a maze of doors, stairwells and offices used by city municipal workers.

In a chaotic scenario, four officers scoured the building, searching for the shooter. They discovered him on the building's second floor and engaged him in a gunbattle. The suspect fired numerous shots through an office door and wall toward the officers before the gunfire stopped, Cervera said.

That's when officers decided to enter the office and engage the shooter. "That’s not an easy decision to make," Cervera said. "There’s an individual on the other side of the door. He has a gun. He just shot one of your officers."

Police found Craddock alive but wounded and began administering first aid. The suspect died en route to the hospital.

Cervera said the shooter used a .45-caliber handgun with a silencer that police suspect was used to keep victims from knowing where the attacker was in the building.

That could explain why survivors said they were caught off guard and initially puzzled by what was happening. One described hearing something that sounded like a nail gun. The attacker brought numerous extended magazines, which carry more rounds than traditional ones.

“Clearly this was an individual who did understand and have experience with firearms and had given potentially some forethought into the advantage that using a suppressor would offer him, particularly the suppressor coupled with the caliber of weapon he was using,” said Thor Eells, executive director of the National Tactical Officers Association and a retired law enforcement officer with the Colorado Springs Police Department, where he oversaw a SWAT division.

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The image of a public works employee holed up with a silencer and extended magazines engaged in a merciless assault is a far cry from how Craddock's neighbors saw him.

They described Craddock as a car enthusiast, bodybuilder and quiet man.

Amanda Archer, 22, and Cassetty Howerin, 23, lived in a Virginia Beach town home beneath Craddock for the past year and got to know him only in passing, exchanging the occasional greeting.

“He wasn’t much of a talker,” Archer recalled. “He’s a mystery to us. He’s a mystery to everybody, apparently.”

To avoid excessive publicizing of the shooter's name, officials said they would give his name publicly only once and would refer to him afterward only as "the suspect."

He served in the Army National Guard, according to a newspaper clip from the time of his city hire, and received basic military training and advanced individual training at Fort Sill, Oklahoma.

The Federal Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) said he legally bought two .45-caliber handguns – in 2016 and 2018. Both were found at the crime scene, and neither was used in any other crime, the ATF reported.

Hansen said all but one of the victims were employees of the city working in the public works department. The shooter killed his first victim in a car in the parking lot before he entered the building.