I'm going from memory here, but wasn't there a slingshot purchase listed in a discovery document?
Just spitballing here, but is it possible what really happened was the slingshot was used to bust a window and thus bringing CRSR to the door--and the W4 are just making up the story about a fake drug deal ruse?
Not sure I really believe that is what happened. Just trying to sort this all out in my head so the gears in my brain will quit grinding...
ETA: But, the drug deal ruse does make much more sense now that I think about it. It also ties in with the money scattered near KR's body, making it look like a drug deal gone bad. Just my very confused opinion...