WASHINGTON - The US Navy contractor identified as the gunman in the mass shootings at the Washington Navy Yard had been suffering a host of serious mental issues, including paranoia and a sleep disorder, according to law enforcement officials. He also had been hearing voices in his head, the officials said.

Aaron Alexis, 34, had been treated since August by the Veterans Administration for his mental problems, the officials said. The Navy had not declared him mentally unfit, which would have rescinded a security clearance that Alexis had from his earlier time in the Navy Reserves.

Family members told investigators that Alexis was being treated for his mental issues.

Only a month ago, Alexis, the gunman, was suffering from hallucinations so severe that he called the Newport Police Department in Rhode Island where he told officers he was on business, according to media reports.

When officers came to his hotel room on Aug 7 at 6 am, Alexis told them that he had gotten into an argument with someone at an airport in Virginia. He said the person he had argued with “had sent three people to follow him and to keep him awake by talking to him and sending vibrations to his body” via a microwave machine, according to a police report.

Alexis had moved to three different hotels in a single night to elude strange voices and people he believed were sending the microwave vibrations, the reports said. At a hotel at a nearby naval base, Alexis told the police that he had heard “voices speaking to him through the wall, flooring and ceiling,” said Lt William Fitzgerald of the Newport police.

Alexis told officers that he ‘had never felt anything like this before’, and that “he was worried these people were going to harm him,” Lt. Fitzgerald said.

“He said he never had a history of mental illness,” Lt. Fitzgerald said.

The police told Alexis to stay away from the individuals he believed were following him. “No further action was required,” Lt Fitzgerald told reporters Tuesday reading from the police report.

Still such incidents seemed to be part of a pattern. One official said that Alexis had been exhibiting symptoms of mental illness since at least his early 20s, before he joined the naval reserve and then went on to be a military contractor. The official said Alexis has been described by people who knew him as paranoid and delusional. It is not clear whether Alexis sought medical treatment.

On Monday, Alexis entered the Navy Yard, a secure military facility near the Capitol, killing at least 13 people before he was fatally shot by the authorities. The police say Alexis acted alone. On Tuesday, the authorities said it had taken only two minutes for officers armed with AR-15s to arrive at the Navy Yard once they received the first of many 911 emergency calls.

The authorities said that while they had originally believed that Alexis had been armed with an AR-15 that they now believe he entered the navy yard with only a shotgun and had obtained a pistol once inside.

Navy officials said that although he had shown a “pattern of misbehaviour,” which included insubordination and unauthorised absences, Alexis was given an honourable discharge from the military in January 2011 after he had applied for an early discharge under the Navy’s “early enlisted transition programme.”

Those issues had led the Navy to consider forcing Alexis out of the service with a less than honourable discharge, a law enforcement official said Tuesday.