VIRGINIA BEACH, Va. (AP) -- Officials in Virginia Beach say they have no time frame for when the investigation into last month's mass shooting will be completed.
The city said in a statement Thursday that investigations of similar mass shootings have taken six to 10 months to finish.
Civil engineer DeWayne Craddock opened fire in a Virginia Beach municipal building May 31. He killed 12 people and injured others, including a police officer.
Craddock died in a gunfight with police.
Virginia Beach officials said city police officers and federal agents have dedicated thousands of hours to the investigation. More than 300 interviews have been conducted. They've also reviewed thousands of emails and executed 20 search warrants for anything from cell phones to medical and financial records.
Authorities have not given details on any possible motive.