WASHINGTON — As more information trickled out about the Navy Yard shooter today, gun-control advocates noted an upcoming shift in their congressional strategy.

The FBI battled back against a story that the Aaron Alexis, who killed 12 in the Monday morning rampage, used an AR-15.

“In regards to the weapons used by Mr. Alexis, there has been a lot of information circulating in the media over the past day,” Valerie Parlave, assistant director in charge at the FBI Washington field office, said at a press conference. “Once again, we caution against obtaining information from unofficial sources, and we ask that all inquiries be directed to the FBI.”

“At this time, we believe that Mr. Alexis entered building 197 at the Navy Yard with a shotgun. We do not have any information at this time that he had an AR-15 in his possession,” Parlave continued. “We also believe Mr. Alexis may have gained access to a handgun once inside the facility and after he began shooting. As previously mentioned, Mr. Alexis had legitimate access to the Navy Yard as a result of his work as a contractor, and he utilized a valid pass to gain entry to the building.”

The portrait that emerged of Alexis showed a man with anger-management issues who had experienced scrapes with the law including disorderly conduct, shooting out tires over a parking dispute and shooting through the ceiling of his apartment into another unit.

Perhaps the most alarming account to emerge, though, was the release of a Newport, R.I., police report from Aug. 7 in which the traveling contractor told officers he summoned to his hotel that voices through the wall were threatening him.

The report says Alexis thought three people were sent “to follow him and keep him awake by talking to him and sending vibrations into his body.” He also told cops that he didn’t have mental illness.

The Newport police faxed a copy of the report to naval station police the same day; the sergeant in charge said the naval cop on duty told him they would “follow up on this subject and determine if he is in fact a naval base contractor.” Six weeks later, Alexis bought a Remington shotgun and ammunition in Virginia and, two days later, entered the Navy Yard in D.C. where he went on his shooting spree.

Alexis reportedly tested an AR-15 at the gun store, but was prohibited from buying it because he was from out of state.

A champion of the Senate gun-control effort after the Newtown shooting made clear today that proponents of stricter laws would lead with the revelations of Alexis’ apparent paranoia and delusions.

Sen. Richard Blumenthal (D-Conn.) said on the Senate floor today that “the shooting at the Washington Navy Yard makes clear that, as we said in the wake of Newtown, these kinds of mass killings can happen anywhere, any school, any community – in Newtown, the quintessential New England town or at the Washington Navy Yard, a supposedly secure military facility.”

“And we need to make sure that it happens nowhere. Let us make a mental health initiative, a centerpiece of this renewal and reinvigoration of our effort to stop gun violence,” Blumenthal continued. “Let us combine it with background checks and other commonsense measures. Bring back this issue and these measures. We are not going away. We are not giving up.”

Another proponent of the original gun-control effort this Congress said he still wants to push for an assault weapons ban and limits on ammunition capacity, but also stressed the mental health angle.

“We must take steps to strengthen our mental health system so that individuals who need help with mental illness can get appropriate help and not have access to hand guns or other weapons,” said Sen. Ben Cardin (D-Md.). “Despite lobbying efforts to the contrary, I know that we can protect our communities while still protecting the Constitutional rights of legitimate hunters and existing gun owners.”

Gun-control proponents incorporated the question of sales to those with mental conditions into their efforts after the Newtown shooting — but opted to focus more on the type of weapon than the person behind the gun. Additional restrictions on those who have been seen for mental health issues wades into a stickier debate of determining which conditions would have to be reported and who makes a determination that a person isn’t mentally stable enough to purchase and possess a gun.