Fort Lewis was one of the haunts of the Beltway Sniper who terrorized the DC metro area in 2002.
Hmmm. While investigators will, of course, need to consider all options, for starters, two likely possibly sources of influence for this crime come to mind immediately: Muslims and/or Mexican Gangs. The difference between the two is moot, as it has been demontrated that Hezbollah now apparently operates fairly freely south of the US border.
As I am just jumping, in I realize others have already made similar points — but this bears repeating, I would say!