Navy Yard gunman’s sister on opportunities missed (VIDEO)

In a “CBS This Morning” exclusive interview with the sister of the Washington Navy Yard gunman shed light on the mental health problems that consumed her brother.

Naomi Alexis describes her brother as one with a dark and dangerous past — a past so haunting that she and her sister weren’t surprised when they found out Aaron Alexis was the shooter.

Aaron Alexis shot and killed 12 people on Sept. 16, 2013, at the Washington Navy Yard, in southeast Washington, D.C. The 34-year-old used a valid temporary ID to get into Building 197, and was eventually shot dead himself by police.

FBI agents later found a note from Alexis claiming that “ultra-low frequency” waves had been attacking him for months.

[ CBS News ]