The U.S. Navy was reportedly warned last month that Aaron Alexis, the Washington Navy Yard gunman authorities say killed 12 people in a 30-minute shootout on Monday, said he had been “hearing voices” and may have had signs of mental illness. 

Reuters reported that “police in Newport, Rhode Island, were so concerned about Alexis’ behavior on a business trip there in August that they alerted Navy police,” who promised them they would check if Alexis was a Naval base contractor. 

However, Alexis still obtained a “secret” security clearance that he used to enter the premises on Monday before he went on the shooting rampage that eventually led to his death.  

According to Reuters, “a spokesman said the Navy was looking into the matter, without confirming any details,” and the “Pentagon said it would review security at military installations around the world” after Monday’s incident. 

On that trip to Rhode Island, Alexis told police he felt people were following him and using a “microwave machine” to send vibrations into his body from the floor and ceiling of his hotel room. He also reported hearing multiple voices in his head. 

“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 reportedly wrote in a report that he faxed to the Navy police.

This information comes to light after it was revealed that Alexis was given an honorable discharge “despite a series of eight to 10 misconduct charges, ranging from traffic offenses to disorderly conduct.” This news comes after a “Defense Department Inspector General’s report published on Tuesday revealed security lapses that allowed 52 convicted felons to gain access to Navy facilities.”