“At this time we believe that Mr. Alexis entered building 197 at the Navy Yard with a shotgun,” Parlave said. “We do not have any information at this time that he had an AR-15 in his possession. We also believe that Mr. Alexis may have gained access to a handgun once inside the facility and after he began shooting.”

Early reports incorrectly indicated that Alexis might have carried a semi-automatic assault rifle. Some lawmakers, including Senate Majority Whip Dick DurbinDick DurbinDem senators accuse Trump of purposefully holding back information The GOP must fight against the Durbin amendment's price controls It’s time to rethink prisoner re-entry MORE (D-Ill.), cited the weapon in calls to renew the gun control debate.

The FBI is still investigating Alexis’s past medical history, and said it would not comment on reports that he suffered from serious mental health issues, including paranoia and a sleeping disorder.

Sen. Dianne FeinsteinDianne FeinsteinFeinstein: Comey memos 'going to be turned over' Judiciary chair may call for meeting with Mueller Dem senators accuse Trump of purposefully holding back information MORE (D-Calif.) had pushed for the reinstatement of an assault weapons ban earlier this year after the Newtown, Conn., school shootings, in which an assault rifle was used.

But that proposal failed to make it into a larger gun control package that included a compromise on universal background checks.

Both the background check legislation and the ban on assault weapons were rejected in votes by the Senate earlier this year.