More disturbing details are emerging about the fragile mental state of the gunman who killed 12 people and injured eight in the Washington Navy Yard this week.

Police in Newport, R.I., said what they learned from a phone call from the former naval reservist on Aug. 6 was serious enough for them to alert officials at a naval base in that city.

Aaron Alexis called police in Newport from the Marriott Hotel to report he was hearing voices. Police said they in turn alerted officials at the Newport Naval Station.

According to police, Alexis said he couldn't sleep. The voices were harassing him, wanting to harm him. He believed people were following him, using a microwave machine to send vibrations to his body.

Washington Navy Yard

A police officer stands at the main gate of the Washington Navy Yard in Washington, on Tuesday. (Jason Reed/Reuters)

He said he had changed hotels, moving to one located on the Newport naval base, before ending up at the Marriott, where he summoned police to tell them he couldn't get away from the voices.

People were following him, he claimed, and he was worried the individuals were going to harm him.

Police said they questioned Alexis on whether he had a mental illness and he said no. They could find no history of police reports on episodes that would indicate he had a mental illness.

Police said when they notified the base to relay events at the hotel they were told by the navy police that they would follow up on the matter. It's not clear whether they did.

Also in August, Alexis was treated by by Veterans Affairs for unspecified mental-health issues. According to unidentified officials who spoke to The Associated Press, he had been suffering from paranoia and insomnia.

Alexis, 34, one of the 13 people confirmed dead in Monday morning's shooting in Washington, D.C., had landed in trouble with police for illegally firing guns — first in Seattle in 2004 and then in Fort Worth, Texas, in 2010.

Played violent video games almost non-stop

U.K. media reports quote friends of Alexis in Fort Worth as saying he would play violent video games, including Call of Duty, for up to 18 hours a day and that he would carry a .45 handgun at all times.

His last known address was in Fort Worth, but his roommates say he moved out five months ago.

His father, who lived in New York during the Seattle shooting arrest, told detectives his son had anger management problems related to post-traumatic stress brought on by the attacks of Sept.  11, 2001.

Alexis received a general discharge from the reserve in 2011 after a series of misconduct issues, according to a navy official who spoke anonymously. The official declined to provide details on the types of misconduct in Alexis's record. 

A brief, official bio released by the navy indicated Alexis served as an electrician. He worked for a company called The Experts, a subcontractor for an HP Enterprise Services military contract, Hewlett-Packard said.

On Saturday, Alexis visited Sharpshooters Small Arms Range in Lorton, Va., 28 kilometres southwest of the U.S. capital. He rented a rifle, bought bullets and took target practice at the 16-lane indoor range, then bought a shotgun and 24 shells, according to the store's lawyer.

Two days later, as the workweek dawned, Alexis entered the sprawling Washington Navy Yard, a labyrinth of buildings protected by armed guards.

Authorities believe he drove a rental car there. He was equipped with his pass for base access, and a shotgun. Within minutes, he would create mayhem.

He stepped inside the massive Building 197, housing some 3,000 employees. He opened fire around 8:15 a.m., raining shotgun blasts down from a fourth-floor overlook and third-floor hallway into a glass-walled cafeteria where employees were eating breakfast.

With files from The Associated Press