She (the ex) may have been in Tacoma too at some point, but she ended up in the DC area, that's why the shooting spree was there. The plan may have been to kill her, and the other victims were just to hide her murder in the others and make it look random.
She was certainly in Tacoma for some time. I think her sister or good friend (or both)were also there, and it was she who had custody of Malvo (the young shooter). The older shooter (something "Muhammad") killed one of them while in Tacoma (I forget which one). As I recall, authorities think he also killed one or more women in Baton Rouge, as well.
Well... looks like my gang theory is blown. Looks like the "teen angst" gambit. Loser who thinks the world must "feel his pain", yada yada yada...
Plenty of self-esteem, at any rate. Only somebody pretty arrogant thinks that the world should be interested in his pain in the first place.