D.C. Police Officer Dorian DeSantis, pictured during a reception before he was awarded Officer of the Year, has been cleared in shooting Navy Yard mass killer Aaron Alexis last year. (Sarah L. Voisin/The Washington Post)

The U.S. attorney’s office announced Wednesday that prosecutors have cleared all local and federal police officers who shot at the Navy Yard gunman, including two who inflicted fatal wounds that ended Aaron Alexis’s deadly rampage in September.

Authorities had been waiting for the ruling to close the books on open inquiries into the police actions during the 69-minute standoff at Building 197, where Alexis fatally shot 12 civilians. Ten were dead in the first six minutes; two more in the next 16 minutes.

D.C. Police Officer Dorian DeSantis and U.S. Park Police Officer Carl Hiott fired on Alexis, 34, as he emerged from under a desk amid a maze of cubicles on the third floor and shot at them from a few feet away. That final confrontation came shortly after Alexis shot D.C. Police Officer Scott Williams in each leg.

DeSantis was struck in the chest but the bullet lodged in his protective vest, and he didn’t realize he had been hit until a day or two later. Alexis was pronounced dead on the scene.

“After a careful review of the evidence, we have closed this investigation,” U.S. Attorney Ronald C. Machen Jr. said in a statement. “We concluded that the law enforcement officers involved demonstrated exceptional valor in acting to protect the lives of Navy Yard employees and other responding law enforcement officers.”

Aaron Alexis (AP)

Other officers, including those with Naval Criminal Investigative Service, had fired at Alexis earlier in the standoff and were among those cleared Thursday. A total of eight officers discharged weapons inside the building.

Spokesmen for the U.S. Park Police and D.C. police said DeSantis and Hiott have returned to duty. Officials had little doubt the officers would be cleared in the shooting, but the magnitude of the mass killing and the enormity of the crime scene — a more than 600,000-square-foot building with room for 3,000 workers — took months to process.

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. He took an elevator to the fourth floor and walked to the men’s room, where police said he assembled a Remington 870 shotgun. He left the men’s room at 8:16 a.m. and began shooting, killing three people in less than four minutes.

During his rampage, he fatally shot a retired Maryland State Police trooper who was working as a security officer and took his handgun. The FBI has said Alexis was driven by delusions and thought he was being controlled by low-frequency radio waves.

The shooter’s mental state and how he acquired security clearances despite prior run-ins with law enforcement have been a point of criticism.

Last month, D.C. police released an exhaustive self-review of how the department reacted to the mass shooting, which included several break-downs in communication with other agencies, in particular the Navy. None of the failures led to the loss of lives, police concluded, but they might have helped officers find Alexis sooner and prevented an officer from being shot and seriously wounded.

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