From the NYT:

Suspect’s Past Fell Just Short of Raising Alarm 

... As an honorably discharged veteran, he cleared a basic hurdle to receive a Defense Department security pass. Despite his being investigated by police departments in Seattle and Fort Worth, for firing a gun in anger, no charges were filed that would have shown up in his F.B.I. fingerprint file. .... Mr. Alexis was also twice investigated by other police departments in shooting episodes — once for firing through his ceiling in Fort Worth, Tex., and another time for shooting out a car’s tires in Seattle, during what he described as an anger-fueled blackout.