WASHINGTON (WJLA) - Law enforcement officers engaged with Washington Navy Yard shooter Aaron Alexis on multiple occasions during his Monday morning shooting rampage before he was finally killed, authorities said Tuesday.
A day after the 34-year-old Fort Worth, Texas resident and Navy veteran took 12 lives at the historic Navy Yard, federal, local and Naval officials say they're still working to figure out what motivated Alexis' horrific actions.
FBI Assistant Director Valerie Parlave, along with officials from numerous law enforcement agencies, said Tuesday that their investigation into the mass shooting has moved into a phase of evidence recovery - a "methodical, time-intensive" process that will take weeks, if not months.
"We will remain there as long as necessary," Parlave said.
Thirteen people, including Alexis, were killed Monday after Alexis burst into Building 197 at the Navy Yard and opened fire indiscriminately. Parlave said Alexis had a shotgun when arrived and likely gained access to a handgun during the assault.
The shooting killed 12 civilian and contract workers, all of whom were between the ages of 46 and 73. It stands as the largest shooting on a military installation since the 2009 incident at Fort Hood in Texas.
Refuting earlier reports, Parlave said that the 34-year-old Fort Worth, Texas resident did not have an AR-15 assault rifle. Sources also told the Associated Press Tuesday that Alexis had previously been treated for mental illness, including the fact that he had "heard voices."
Federal officials continue to try to piece together Alexis' recent movements, but Parlave did say that the shooter arrived in the D.C. area on or around Aug. 25, at which point he began working for The Experts, a federal subcontractor. The access granted to him allowed him on the Navy Yard grounds.
Authorities say he stayed at multiple hotels throughout his time in Washington, including most recently at the Marriott Residence Inn on E Street Southwest.
D.C. Police Chief Cathy Lanier continued to laud her officers actions to save additional lives at the Navy Yard, saying that officers from multiple jurisdictions were at and inside Building 197 - the home of the Naval Sea Systems Command - within 7 minutes of an initial call of shots fired.
"Our officers heroically went into a building, witnessing multiple casualties, while pursuing and engaging a gunman determined to kill as many people as possible," Lanier said. "The officers who responded did an incredible job."
Ofc. Scott Williams, the officer who was shot in the leg during Alexis' shooting spree, is said to be in good spirits at MedStar Washington Hospital Center, where he continues to recover from his injuries. Lanier said that Williams is likely to make a full recovery.
Lanier also defended her department's order for local residents in and around the Navy Yard area to shelter-in-place for an extended period of time while they investigated the possible presence of two additional shooters.
Both of those shooters, described as a white and black male, both wearing military uniforms and between the age of 40 and 50, were both discredited as suspects by 10 p.m. Monday.
"We erred on the side of caution," Lanier said. "It was the right decision. We had to run down some additional information."
Ron Machen, the U.S. Attorney for the District of Columbia, says that his agency's main purpose at this point is to answer the many questions left open after the shooting.
Those questions include how Alexis got access to his weapons and if anyone aided him, either knowingly or unwittingly.
"We're not going to stop until we get answers to those questions," Machen said. "It's important to the loved ones lost."
According to a lawyer representing Sharpshooters, a small-arms range in Lorton, Alexis visited the Terminal Road range this past Saturday and fired off rounds from a rented rifle at their practice range.
He then purchased a Remington 870 shotgun and about two boxes of ammunition, attorney J. Michael Slocum says. His information was entered into the National Instant Criminal Background Check System, which approved him to purchase the weapon.
In a statement, Sharpshooters confirms:
Sharpshooters fully complies with all requirements to conduct background checks on all potential purchasers as required by law.
It's not known whether or not that gun was used during Monday's massacre.