Authorities in the U.S. say the gunman who went on a shooting spree at a naval base in Washington D.C. - leaving 13 people dead - was a former Navy reservist.
34-year-old Aaron Alexis was discharged in 2011 after a series of misconduct issues.
It has emerged that the 34 year old had special clearance to be there as he was working as a contractor for Hewlett Packard.
The Mayor of Washington - Vincent Grey - says they're trying to work out what happened:
