WASHINGTON (AP) — A month before he went on the rampage that left 13 dead, Washington Navy Yard gunman Aaron Alexis complained to police in Rhode Island that people were talking to him through the walls and ceilings of his hotel rooms and sending microwave vibrations into his body to deprive him of sleep.The account, contained in an Aug. 7 report from Newport, R.I., police, adds to the picture that has emerged of an agitated and erratic figure whose behavior and mental state had repeatedly come to authorities’ attention but didn’t seem to affect his security clearance.Alexis, a 34-year-old information technology employee at a defense-related computer company, used a valid pass Monday to get into the Navy Yard and killed 12 people before he was slain by police in a shootout that lasted more than a half-hour.A day after the assault, the motive was still a mystery. U.S. law enforcement officials told The Associated Press that investigators had found no manifesto or other writings suggesting a political or religious motivation.Alexis, a former Navy reservist, had been undergoing mental health treatment from Veterans Affairs since August but was not stripped of his security clearance, according to the law enforcement officials, who spoke on condition of anonymity because the criminal investigation was still going on. He had been suffering a host of serious mental problems, including paranoia and a sleep disorder, and had been hearing voices in his head, the officials said.In the Newport, R.I., incident, Alexis told police he got into an argument with someone as he was getting on a flight from Virginia to Rhode Island, where he was working as a naval contractor, and he said the person sent three people to follow and harass him. He said he heard voices talking to him through a wall while at one hotel, so he changed hotels twice, but the voices followed him, according to the report. He said he feared they might harm him.He also “stated that the individuals are using ‘some sort of microwave machine’ to send vibrations through the ceiling, penetrating his body so he cannot fall asleep.”Later that day, Newport police alerted the Rhode Island naval station and sent a copy of the police report, Newport police Lt. William Fitzgerald said Thursday.Alexis came to the Washington area about two weeks later and had been staying at hotels. On Saturday, two days before the attack, he went to a Virginia gun store about 15 miles from the Navy Yard. He rented a rifle, bought bullets and took target practice at Sharpshooters Small Arms Range, the store’s attorney Michael Slocum said. Alexis then bought a shotgun and 24 shells, according to Slocum.The FBI said during Monday’s attack Alexis was armed with a shotgun. Officials said he also took a handgun from a law officer.Alexis had run-ins with the law in 2004 and 2010 in Texas and Seattle after he was accused of firing a gun in anger. He was not prosecuted in either case.And his bouts of insubordination, disorderly conduct and being absent from work without authorization prompted the Navy to grant him an early — but honorable — discharge in 2011 after nearly four years as a full-time reservist, authorities said.Alexis joined the Florida-based IT consulting firm The Experts in September 2012, leaving a few months later to return to school. He came back in June to do part-time work at the Washington Navy Yard as a subcontractor, helping the military update computer systems.The Experts’ CEO, Thomas Hoshko, said that Alexis had “no personal issues,” and he confirmed that Alexis had been granted a “secret” clearance by the Defense Security Service five years ago.Alexis’s clearance — lower than “top secret” — doesn’t need to be renewed for 10 years. Still, the company said it hired outside vendors twice to check Alexis’ criminal history.Alexis’ background check “came back clear,” Hoshko said.———Associated Presss Matt Apuzzo, Adam Goldman, Jesse Holland, Stacy A. Anderson, Brian Witte and Ben Nuckols in Washington contributed to this report.