Alexis continued to walk through the building, blasting away. On the fourth floor, he killed 58-year old Gerald Read, 62-year-old Kathy Gaarde and 53-year old Sylvia Frazier, whom Weaver said "was the nicest person in the world."
At 8:16 a.m., Alexis entered a stairwell and exited on the third floor where he began randomly shooting in all directions. At one point, he reached into his pocket for more shells.
An announcement came over the intercom and told people to evacuate the building because of a "fire emergency," witness Terrie Durham said.
Michael Arnold suffered from an early season cold. He was on the phone with his wife who called to see how he was feeling when an alarm went off. He told her he would call her back, but he didn't get to.
Weaver came out from under his desk and ran. He turned the corner and saw his supervisor, 51-year-old Mary Francis Knight, lifeless on the ground.
He kneeled over her and looked into her eyes "to see if there was consciousness, and there was none."
Weaver saw his friend who had been shot in the finger and side of the head. Weaver downplayed her injuries to comfort her, telling her he'd gotten bigger cuts playing hockey and said, "Let's get out of here."
'Get out of the building now!'
Durham was gathering his belongings. Then he began to move with more urgency when people began screaming, "Get out of the building now! Get out of the building now!"
Durham and three co-workers walked down the hall when they came within eyesight of Alexis. Unaware that Alexis was holding a gun, the foursome continued walking toward him. Alexis stood out because he wasn't moving with the same urgency as everyone else.
"I kept thinking, 'What is he doing? There's a fire in the building. We need to get out,' " Durham said.
Then Alexis opened fire in their direction. Incredibly, he missed.
As Weaver ran down the stairs, he told people to "run for your lives." Once he reached the first floor, he saw a conference room full of people, seemingly unaware of the carnage on the floors above. He told them to get out and "everybody just started scattering."
"People went into a complete panic at that point," Weaver said. He told an officer "there's a guy slaughtering people with a shotgun" on the fourth floor and they "need to get up there with a lot of weapons."
The 911 calls started pouring in. "We have an officer down, Building 197, third floor," one dispatcher said.
Alexis was now on the first floor, where he shot a guard and took his handgun.
While Alexis was on the first floor, Lavern and the security guards made it to the first floor with Pandit, who was still breathing. They heard Alexis was on the west side of the building. They escaped through an alternate exit to a street corner away from Building 197. Pandit was still breathing.
Unaware of the terror unfolding in Building 197, another worker came out to help administer CPR to Pandit, who he thought had suffered a heart attack. Pandit later died from his wounds.
Alexis returned to the third floor. Out of shotgun ammunition, he used the guard's Beretta handgun.
Seven minutes after the first 911 call, officers from Washington Metropolitan Police Department, Naval Criminal Investigative Service and the U.S. Park Police began arriving on the scene and got into what they described as a "running gun battle" with Alexis. He ducked down hallways and ran in and out of offices and conference rooms. Several times authorities thought he was down, but he'd come out firing.
'One of the worst things we've seen'
MPD Chief Cathy Lanier called the crime scene "one of the worst things we've seen in Washington."
"As officers entered the building, they were, you know, making transmissions in and keeping command informed as to what they were coming across as they went through," she said. "Multiple victims. There was gunfire still going on."
By 8:45 a.m., the first tactical teams, better equipped to handle this kind of emergency, began arriving. Not long after that, Alexis was finally down for good.
At 9:30 a.m., 90 minutes after Alexis drove on to the base, he was pronounced dead. He had killed 12 Navy Yard workers and wounded eight others.