U.S. Defense Secretary Chuck Hagel says officials missed "red flags" about Washington Navy Yard shooter Aaron Alexis.
Alexis killed 12 people before being shot dead by police Monday at the Navy facility.
Hagel on Wednesday said there were a lot of red flags on Alexis' past legal problems and mental illness. He said the questions have to be answered about why these warning signs were missed before Alexis got a pass that allowed him to get into the Navy Yard.
Hagel also ordered a security review of all U.S. military facilities worldwide. He said "where there are gaps, we will close them.''
Alexis was arrested in two separate shooting incidents in 2004 and 2010. He was cited several times for misconduct during his four-year Navy service, which ended in 2011.
Alexis also claimed to hear voices and was undergoing mental health treatment at the Department of Veterans Affairs, but was not stripped of his security clearance. That allowed him to be hired as an information technology specialist by a private defense contractor.
His motive for the Navy Yard shootings is still unknown.
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.
OPTIONAL OBAMA SOUNDBITE:
"The fact that we do not have a firm enough background check system is something that makes us more vulnerable to these kinds of mass shootings. And I do get concerned that this becomes a ritual that we go through every three, four months, where we have these horrific mass shootings and yet we're not willing to take some basic actions that we know could make a difference."