Defense Secretary Chuck Hagel is ordering a security review of all U.S. military facilities around the world after a gunman shot 12 people to death Monday at the Washington Navy Yard.
The Pentagon says details of the review will be announced Wednesday.
The Navy Yard gunman, 34 year-old Aaron Alexis, was shot dead by police about 30 minutes after he began the shooting rampage. The FBI says he acted alone and got into the Navy Yard with valid identification. His motive is still unknown but police say there is no evidence of connection to terrorism.
Investigators say Alexis had paranoia, a sleep disorder, and claimed he heard voices. His family says he had sought treatment for his mental problems.
Alexis' employer said he worked on at least six military installations in July and August without incident.
U.S. senators remembered the victims with a prayer and a moment of silence Tuesday. At the Navy Memorial near the Capitol, Secretary Hagel, Joint Chiefs Chairman Martin Dempsey, and Washington Mayor Vincent Gray placed a wreath honoring the men and women who were gunned down.
President Barack Obama has ordered all flags across the country to fly at half-staff through sunset Friday to honor the victims.
Alexis opened fire Monday on employees of the Naval Sea Systems Command, using a shotgun and a handgun he took from a wounded security officer. Authorities say earlier reports he had an assault style rifle were incorrect.
Alexis was a resident of Fort Worth, Texas. U.S. media reports say Alexis had been arrested in two previous shooting incidents, in 2004 in Seattle and in Fort Worth in 2010.