Well, anyone who did the slightest bit of physical work might be described as "muscular build" compared to someone whose job is reviewing security tapes...
I still don't see a conclusive link to the original (alleged) theft of the card and IK... the thief was described as wearing dark clothing, while IK was wearing a light sweatshirt and improvised mask. Obviously what you wear in an Anchorage winter is different from in the Southwest, but it doesn't prove anything - and the gap before the card was used is significant.
The mask makes it obvious he wasn't using the card in good faith, i.e., having been given it in payment for some quasi-legit deal. But if he knew it was stolen but was told it was okay to use, and it was payment for something nefarious, he might have taken steps to protect himself. Even if IK wasn't the sharpest knife in the drawer, he took a route that would allow him to visit ATMs where he would be unlikely to encounter any other customers (the mask look is difficult to pull off without notice), and having established the limit through trial and error, he then stayed under it. If he paid for the flight to Vegas via the card,
Could Sam have been connected to the original theft (as having the PIN is essential to this scenario) but the card have then changed hands? Are the original kidnappers having a good laugh as IK, having received the card in exchange for something (i.e., keys to a house) is now the fall guy?
But if so, what did they tell IK to convince him this was a good idea? If he was the kidnapper, he would have to be an absolute moron to be using the card... not impossible, but improbable.
If he was using the card as a payment, and the name on the card was James Koenig, wouldn't alarm bells go off? But Duane was careful to keep his last name out of the news. If this card belongs to a person close to SK, whose PIN she might know, more likely Duane's than James... If that is the scenario at all.
Sorry, first cup of coffee ramblings.