The U.S. flag is shown lowered to half-staff at the White House. (Photo by Olivier Douliery-Pool/Getty Images)

The shooting at the Navy Yard last September by gunman Aaron Alexis, which left 12 people dead, could have been prevented, a new report from the Department of Defense reveals.

The investigation team, led by Adm. John Richardson, concluded that there were “missed opportunities for intervention” in identifying Alexis as a security threat because his life “[demonstrated] a pattern of misconduct and disturbing behavior,” the Post reports. According to the report, which was unveiled by Defense Secretary Chuck Hagel at a press conference this morning, The Office of Personnel Management gave Alexis clearance although it “was missing critical information” about his past mental health. Furthermore, Alexis’ superiors apparently didn’t record “multiple incidents of adverse behavior during is tim on active duty.” From the Post:

As a result, managers at The Experts, Inc., the firm that employed Alexis, “had no insight into Alexis’ chronic personal conduct issues during his Navy service” when they recruited him for a position that required a security clearance, the report said. The firm, the Pentagon review contends, failed to “report behaviors indicating psychological instability,” to the proper authorities.

In a statement, Secretary of the Navy Ray Mabus said that “safeguarding our people remains critical to our national security. Through all of the actions taken as a result of the investigation, we seek to improve our ability to protect our people, and reduce the likelihood that events like this will happen again.”

You can read the full report here.