The Virginia Beach employee who shot and killed 12 people at a municipal building gave no hint of the bloodbath to come when he emailed his resignation letter earlier in the day, saying that he was leaving for "personal reasons" but that "it has been a pleasure to serve."

The two-sentence email from DeWayne Craddock, an engineer with the city utilities department, was released Monday.

Craddock, 40, opened fire on his co-workers on Friday, then was killed in a gunbattle with police, leaving no immediate clues to what set him off.

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

An unidentified person responded to the email by saying he or she hoped that Craddock would be able to resolve his personal issues and that Craddock's last day would be Friday, June 14. Craddock responded: "Thank you. Yes, that is correct."

Authorities shed no immediate light on what led him to resign.

Craddock was an employee "in good standing" and showed "satisfactory" job performance, City Manager Dave Hansen said.

That has left survivors, officials and community members wondering what set off the violence.

"Right now we do not have anything glaring," said Police Chief James Cervera. "There's nothing that hits you right between the eyes. But we are working on it."

On Monday, a makeshift memorial made of bouquets, flags, teddy bears and crosses bearing the names of the shooting victims stood at one entrance to the municipal center. A small group of city employees wept and hugged each other as they left flowers by one of the crosses. Volunteers with comfort dogs were on hand.

Crystal Pangelinan came to pay her respects after her children, ages 5 and 7, went to school.

"Explaining what happened to them was hard," she said.

The building is part of a sprawling compound of government buildings. While other buildings appeared to be open for business Monday morning, signs of the shooting remained. A section of the compound remained blocked off by law enforcement vehicles, and FBI personnel could be seen walking around.

There was no indication Craddock targeted anyone specifically.

The police chief said investigators are retracing the gunman's activities on the day of the attack, using his electronic keycard to track his movements through secure areas of the building. They are also reviewing his personal and professional lives.