On Sept. 16, 2013, Aaron Alexis walked into Washington, D.C.'s, Navy Yard complex and opened fire. He killed 12 people and wounded four before he was fatally shot by police. Here's a timeline of how the shooting rampage unfolded that day. (Gillian Brockell/The Washington Post)

Communication problems among federal and local authorities complicated the search for the gunman during September’s deadly mass shooting at the Washington Navy Yard, according to a D.C. police report that says city officers were unable to make use of live video of the shooter as they streamed into harm’s way.

The report says the U.S. Navy failed to tell police commanders that a video feed from 160 cameras in the corridors where Aaron Alexis, 34, opened fire could be accessed from a room just inside the building. A private security guard had locked himself in the room and apparently did not try to contact anyone.

Too many command buses crowded the scene, officers talked over each other on different radio channels, and there was confusion among some responders — and even top officials — about who was in charge.

“We never saw the base commander during the entire incident,” D.C. Police Chief Cathy L. Lanier said in an interview. She said Navy officials set up a separate command center. “We’re still not sure who was the right person to be the decision-maker,” Lanier added. “It should have been the person in charge of the base.”

Access to the video feed probably would not have saved any lives on Sept. 16 — 10 of the 12 victims were killed within the first six minutes, before the first active shooter teams entered — but it might have prevented Alexis from wounding a police officer, Lanier said. It would also have allowed police to more quickly discount reports of a possible second shooter. Authorities kept a swath of the District in lockdown and on edge for three hours after officers fatally shot Alexis, who was acting alone.

Lanier said she does not know why the security guard in the video room did not notify anyone. “The only thing we can assume is that the person froze, didn’t know what to do,” the chief said.

A spokeswoman for Navy District Washington did not respond to specific questions raised in the report about the base commander or the security guard, who was not identified. “I can tell you that the Navy Yard leadership is working closely with [D.C. police] to strengthen our ties and to further develop our joint procedures during crisis situations,” according to a statement from the spokeswoman, Chatney Auger. She said there are ongoing discussions with police “to improve response efforts.”

The 82-page report — intended to scrutinize law enforcement’s response and help D.C. police and other agencies prepare for future attacks — was obtained by The Washington Post under a Freedom of Information Act request. It details Alexis’s movements as well as the heroics of officers and Navy Yard workers over 69 harrowing minutes. It praises the cooperation between officers from myriad agencies who entered the building in teams — 117 officers in all — but highlights flaws in the coordination at the command level.

The report echoes some problems raised after the 9/11 terrorist attacks, including the inability of all responders to talk to each other over their radios. Although some kinks have been worked out in recent years, such massive, multilayered responses are still difficult.

With several agencies setting up command centers outside the 600,000-square-foot building, some critical information did not reach D.C. police officials who were directing the vast response, the report concludes. That included floor plans for Building 197: They were in a Homeland Security command bus just feet away, but they never got to Lanier.

The report’s authors stress that on the morning of the shooting, officers and commanders were making instantaneous decisions in a deadly situation. Authorities did not know how many shooters there were, and early reports suggested that it could have been two or even three. Police initially encountered locked gates and located Building 197 only because hundreds of people were running out of it. The first officers inside took a slain security guard’s badge, which gave them access to many locked sections, and propped open doors for others who followed.

“The actions and decisions of that day were made, often in a split second, in a dynamic and extraordinary environment under extreme duress, facing a multitude of unforeseen challenges and dangers, without the benefit of hindsight,” the report says. But, the report stresses, access to live feeds during the 69 minutes “may have also allowed police to quickly identify the shooter, ascertain his location, and help in determining whether others may have been involved.”

The report recommends 76 changes in training, policy and equipment. It found that the AR-15 assault weapons officers carried were too long and unwieldy in the close office confines, so police will also be getting shorter-barrel M4 rifles. Scott Williams, a D.C. officer who was shot in the legs, believes that radio transmissions gave away his location, leading to plans to have officers now wear earpieces. And officers realized that the formation they’d been taught to use to hunt active shooters didn’t work in the narrow hallways and cubicle mazes.

No officers, officials or victims are named, but some of their identities are known through previous reporting.

Alexis, a contractor who had worked at the Navy Yard in information technology for a week, walked into Building 197 at 8:08 a.m., using his key card at the main entrance. He took an elevator to the fourth floor and walked to the men’s room, where police said he assembled his Remington 870 shotgun. He left the men’s room at 8:16 a.m. and started shooting, killing three people in less than four minutes. He killed others on a different floor; by then, police were streaming into the building.

He was fatally shot by police at 9:25 a.m. The FBI has said Alexis was driven by delusions and thought he was being controlled by low-frequency radio waves. Police noted in the report that Alexis’s demeanor changed after he knew that police were closing in. “He has gone from hunter, to hunted,” the report says.

Lanier attributed some of the problems to well-intentioned reforms made after shootings at Fort Hood in Texas, which called for military bases to set up their own emergency call centers, similar to 911. In this case, it created confusion, because the calls from workers who described Alexis and his whereabouts didn’t go to a single, central location, the report says.

Unlike many military bases, Lanier noted, the Navy Yard is more like a typical office complex. Its 14,000 workers are mostly civilians and unarmed, including the 3,000 in Building 197, and they’re protected by a small Navy police force that had just six officers on duty at the time of the shooting.

“This military base sits in the middle of a major metropolitan city that has a very large and well-trained police force,” Lanier said. “This military base doesn’t have a large armed presence.” But, she added, “we’re just as guilty on our side for making the assumption that we’d never have to go in there and defend the base.”

The report notes close encounters with workers who narrowly escaped Alexis. It details the actions of police officers, including Williams, who led a four-person team, and Dorian DeSantis, who along with a U.S. Park Police officer killed Alexis during the final firefight. A bullet struck DeSantis in the chest, but he was saved by his police vest.

Live video “may have saved Scotty,” Lanier said. “It may have saved Dorian from being shot. I don’t think it would have prevented the final confrontation with Aaron Alexis. I think that was the final confrontation that Aaron Alexis wanted.”

Lanier said there was a Navy official in her command center police thought was a liaison with higher-ranking authorities. But that turned out to be wrong.

The report says that someone in the building told police that he or she had seen a man wearing tan miliary-style clothing holding a gun at his hip, which sparked a search for a second shooter.

When police got access to video from external cameras partway through the incident, they saw two men outside the building, one in tan clothing holding what looked like a gun. On the video, Lanier said, “we see this guy drop. He’s been shot. The other guy runs.”

Police thought they had just seen the second gunman. But three hours later, when the interior camera feed was finally obtained, they saw what wasn’t available before: Alexis stepping out of a doorway and shooting, hitting the man in the head from 100 yards away.

Authorities then concluded that Alexis had acted alone.

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