Suspected Virginia Beach shooter used legally-bought gun suppressor DeWayne Craddock is suspected of killing 12 people at his Virginia workplace.

The public utilities engineer who allegedly gunned down 12 people, including 11 colleagues, at the Virginia Beach Municipal Center, emailed his boss that he was resigning just hours before he committed the massacre with legally-bought pistols and a gun suppressor, officials said.

Investigators said DeWayne Craddock, 40, used two .45-caliber pistols, extended ammunition magazines and a gun suppressor in the rampage. Both guns and the suppressor, according to investigators, were purchased legally by Craddock.

He bought one of the pistols in 2016 and the other in 2018. It was unclear when he purchased the gun suppressor.

Virginia Beach Police Chief James Cervera told ABC News that the suppressor does not eliminate the sound of gunfire, but he could not say whether the use of the device had any impact on the death toll in Building 2 of the Virginia Beach Municipal Center.

Two other guns seized from Craddock's home were also purchased legally, officials said.

In the short resignation email, Craddock telecast nothing of the horror that was to come on Friday afternoon.

"I want to officially put in my (2) weeks' notice to vacate my position of Engineer with the City of Virginia Beach," Craddock wrote in the email. "It has been a pleasure to serve the City, but due to personal reasons I must relieve my position."

Craddock did not elaborate on what his personal issues were.

The name of the person to whom the email was sent was redacted by officials. The recipient of the email wrote back, telling Craddock, "I hope you are able to resolve your personal reasons. To be clear, your last work day will be Friday, June 14, 2019."

Virginia Beach City Manager Dave Hansen said Craddock was in "good standing" at work and had no ongoing disciplinary issues. Hansen said Craddock's latest work evaluation showed he had a "satisfactory" job performance.

Police investigating the massacre have yet to release a motive for what may have prompted the bloodshed. Craddock was killed after a prolonged gunfight with police.

"We continue to speak with witnesses, and others who may have information," a police spokesperson told ABC News on Monday. "It is still in the early stages of such a large investigation. Additional details, if obtained, will be shared once we reach a point where it will not jeopardize the investigation.”

Investigators said Craddock, who was single and lived alone, worked as a public utilities engineer in Virginia Beach for 15 years.

Just after 4 p.m. on Friday, he allegedly went on the rampage. Craddock allegedly shot and killed one victim outside the Municipal Building, then entered the four-story Building 2 and continued the massacre, using his security pass to swipe his way into inner offices and conference rooms, Virginia Beach police officials told ABC News.

After killing five women and seven men, including a private contractor who was there to file a permit, Craddock got into a gunfight with police that left him dead and one Virginia Beach Police officer hurt.

On Sunday, police said the first 911 calls of the shooting were made at 4:06 p.m. and that two officers arrived at Building 2 in two minutes, running there from a police station across the street.

Within five to 10 minutes after entering the building, at least four officers located and engaged the suspect on the second floor of the building.

The suspect fired as he moved through numerous office spaces. During the gun battle, doors were closed and locked, and people who were still on that floor were sheltering in place.

At one point, the gunman was shooting at officers through a closed door. Once the gunfire subsided, officers breached the door and found the suspect mortally wounded.

The victims slain in the massacre were identified as Richard Nettleton, a public utilities engineer for 24 years; Laquita C. Brown of Chesapeake, a public works right-of-way agent for 4 1/2 years; Tara Welch Gallagher of Virginia Beach, a 6-year public works engineer; Mary Louise Gayle of Virginia Beach, a public works engineer for 24 years and a right-of-way agent; Alexander Mikhail Gusev of Virginia Beach, a public works right-of-way employee for 9 years.

Also killed were Katherine A. Nixon of Virginia Beach, a public utilities engineer for 10 years; Christopher Kelly Rapp, a public works employee for 11 months; Ryan Keith Cox of Virginia Beach, a public utilities worker for 12 1/2 years; Joshua O. Hardy of Virginia Beach, a 4 1/2-year public utilities engineer technician; Michelle "Missy" Langer of Virginia Beach, a public works administrative assistant for 12 years; and Robert "Bobby" Williams of Chesapeake, a public utilities special projects coordinator for 41 years.

Independent contractor Herbert "Bert" Snelling of Virginia Beach, who was in the Municipal Center to file a permit, was also killed.

Four other victims were wounded in the shooting and remained in hospitals on Monday in critical condition.

A memorial service for the victims is being planned for Thursday.

On Monday, hundreds of city employees returned to work for the first time since the mass shooting. They were greeted by counselors and volunteers with therapy dogs.

Building 2 of the Municipal Center remained closed, and city workers congregated in the Virginia Beach Convention Center.

Hansen, the city manager, spoke to the employees, encouraging them to stick together and work through the tragedy as a "family," Michelle Walz, a supervisor in the city's Parks Department, told ABC affiliate WVEC-TV in Norfolk, Virginia.