I don't know if it's been checked out 100% but they could have been sold on
Ebay
Craigslist
Through a gaming shop
Through local networks
Through any magic the gathering event
my ex used to purchase them at flea markets back in the early 90's from people that were getting out of the game etc.
The card thing throws me though - IF this crowd was bad, and into some questionable behaviors, why not take the car, and have it chopped and shopped? Much more valuable then the cards (The reason I say that is because it would take a "special" buyer..IE someone who WANTS the cards, not just the average/everyday person...even with chop and shop of cars, there's an open market, parts, body work, after market parts, scrap the frame etc..)
The checks..Not sure about bremerton, but I know in Detroit, you can go into places w/ no ID and cash just about any type of check, again, you may have to know someone but if it was the type of crowd that had those connections, someone could have lifted the checks and probably had a nice chunk of change etc.
IMO the cards are maybe just a smoke screen...