More Details Emerge About Navy Yard Gunman

The Washington Navy Yard will resume mostly normal operations Thursday, as investigators continue to look into the background of the man who carried out this week's deadly shooting rampage.

All buildings will reopen on the military complex except Building 197, where Aaron Alexis shot and killed 12 people Monday before he was killed in a shootout with police.

The Department of Veterans Affairs says the former Navy reserve sailor visited two V.A. hospitals just weeks before the shootings, complaining of insomnia. Alexis was prescribed sleep medication during both visits, and told doctors he did not feel depressed or anxious, and was not thinking of hurting himself or others.

Investigators earlier revealed Alexis was undergoing treatment at a V.A. for mental health issues, claiming he heard voices.

Red flags

U.S. Defense Secretary Chuck Hagel says officials missed "red flags," or warning signs, about Alexis' past history of violent incidents and misconduct both before and during his four-year Navy service, which ended in 2011. Despite these signs, Alexis received a security clearance that allowed him to be hired as an information technology specialist by a private defense contractor, and maintained it despite his mental health issues.

Hagel also ordered a security review of all U.S. military facilities worldwide.

Alexis' mother, Cathleen Alexis, issued a tearful statement Wednesday from her home in New York City.

Monday's violence is the latest in a rash of deadly mass shootings in the United States. During an interview on the Spanish language television network Telemundo, President Barack Obama called on Congress to approve new gun control measures to keep guns out of the hands of the mentally ill.

Obama will attend a memorial service for the victims that has been scheduled for Sunday.