Only in that that is where they obtained the rifle. The older guy was (I think) originally from Baton Rouge, La. and the youger one was a "furriner" from one of the Caribbean Islands (Puerto Rico/Dominican Repub.??).
As I recall, the older one married the younger one's mother and got her to the states, where she left him and ended up in or around Tacoma. He followed her up (stalking), and got the younger guy to join him.
There are also strong indications that there was some "Muslim theology" involved.
The mom was Jamaican... right? I do remember some Muslim references at the time... but that was quickly hushed-up.
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.