Two federal law enforcement officials told The Washington Post Tuesday the gunman, Aaron Alexis, had a history of mental illness and was treated by the Department of Veterans Affairs.
J. Michael Slocum, an attorney for Sharpshooters Small Arms Range in Lorton, Va., said in a statement Tuesday Alexis rented a rifle and bought ammunition at the business Sunday, and used it for practice at the range, ABC News reported.
He then provided his personal information to the business as required by federal law and was approved by the system to purchase a Remington 870 shotgun and about two boxes of shells, the network said.
"After the terrible and tragic events at the Navy Yard, the Sharpshooters was visited by federal law enforcement authorities, who reviewed the range's records, including video and other materials," the statement said. "So far, as is known Mr. Alexis visited the range only once, and he has had no other contact with the Range, so far as is known."
Authorities determined Alexis was armed with a shotgun and at least one handgun he took from a guard he shot when he went on the Navy Yard rampage Monday, killing a dozen people and wounding others before being killed while exchanging gunfire with police.
"There is no doubt in my mind they saved numerous lives," Metropolitan Police Chief Cathy Lanier said Tuesday in praising the officers' actions.
ABC said federal investigators were going through Alexis' laptop and his hotel room for clues as to what triggered his shooting spree.
The Post reported its sources, who spoke on condition of anonymity, said Alexis, a former Navy reservist, had told people he was hearing "voices." The newspaper said a police report from last month revealed Alexis called police to his hotel room in Newport, R.I., and told them he was being followed by three people who were keeping him awake "by talking to him and sending vibrations into his body."
An unidentified Navy official told the Post Alexis, 34, who received an honorable discharge effective Jan. 31, 2011, was cited at least eight times for misconduct for various offenses, including insubordination and disorderly conduct, for which he received administrative punishments three times. He also had run-ins with civilian law enforcement agencies.
Valerie Parlave, assistant director in charge of the FBI Washington Field Office, said Alexis had been staying in Washington hotels since about Aug. 25.
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