A District of Columbia police officer was shot in the chest but was saved by his protective vest while responding to the shootings at the Washington Navy Yard, Police Chief Cathy Lanier said Tuesday.

In a television appearance, Lanier said another officer who was shot in the legs during the Sept. 16 rampage was continuing to recover and could be released from the hospital within days.

“In terms of the heroism that was displayed by the officers, we now know that not only was one of our officers shot in the building but another one of our officers actually took two rounds to the chest. It was stopped by his vest,” Lanier said. “We are extremely lucky that we didn’t lose a police officer in there as well.”

The FBI is continuing to investigate the shooting, which began when 34-year-old Aaron Alexis opened fire with a shotgun inside an office building on the grounds of the Navy Yard. He killed 12 people before being slain by an officer during a shootout. The former Navy reservist and IT contractor used a valid badge to gain access to the base, authorities have said. No motive has been revealed.

Funerals for four of the victims were being held Tuesday.

The building where the shooting took place — the headquarters of the Naval Sea Systems Command and home to about 3,000 employees — presented a logistical nightmare for police officers, encompassing nearly 1 million square feet of office space and thousands of high-wall cubicles, Lanier said.

“It’s an absolute worst-case scenario for law enforcement to confront a gunman in that environment,” she said.

Department of Defense officials have acknowledged that a lot of red flags were missed in Alexis’ background, allowing him to maintain a secret-level security clearance and have access to a secure Navy facility despite a string of behavioral problems and brushes with the law.