WASHINGTON/BOSTON - Rhode Island police warned the US Navy last month that Washington Navy Yard gunman Aaron Alexis had reported "hearing voices," raising further questions about how he gained security clearance at the complex where he went on a shooting rampage.
Officials say Alexis, a Navy contractor and former Navy reservist, opened fire at the Naval Sea Systems Command on Monday, killing 12 people before police shot him dead.
The shooting - a mile and a half from the US Capitol and three miles from the White House - sent shockwaves through Washington.
The Pentagon said it would review security at military installations around the world and the White House promised to review standards for federal government contractors.
A Defense Department Inspector General's report published on Tuesday revealed security lapses that allowed 52 convicted felons to gain access to Navy facilities because budget cuts had undermined vetting.
Meanwhile, the US capital paused to remember the victims, aged 46 to 73, who included retirees, parents and a bird lover.
Police in Newport, Rhode Island, were so concerned about Alexis' behavior on a business trip there in August that they alerted Navy police.
Alexis told police he believed people were following him and "sending vibrations into his body," according to a Newport police report.
He told police that he had twice moved hotels to avoid the noise he heard coming through the floor and the ceiling of his rooms, and that the people following him were using "some sort of microwave machine" to prevent him from sleeping.
"Based on the naval base implications and the claim that the involved subject, one (Aaron Alexis) was 'hearing voices,' I made contact with the on-duty Naval Station police," a Newport police officer wrote, adding that he faxed his report of the incident to Navy police.
The Newport police report said Navy police had promised to check if Alexis was in fact a naval base contractor.
Asked for comment, a spokesman said the Navy was looking into the matter, without confirming any details.
In addition, CNN reported that Alexis had contacted two Veterans Administration hospitals recently and was believed to be seeking psychological help.
"Initial reports indicate that this is an individual who may have had some mental health problems," US President Barack Obama told Spanish-language network Telemundo.
"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."
The Navy gave Alexis an honorable discharge despite a series of eight to 10 misconduct charges, ranging from traffic offenses to disorderly conduct.