If he hadn’t financed the heist, would the Big Cheese be guilty of solicitation without being an accomplice?
You mean if he’d merely requested it, or even just suggested it?
I guess that scenario would be the one where he expresses interest in buying the item from them if they were to “acquire” it, but doesn’t put any money down. I would say that he probably wouldn’t be an accomplice then, since he didn’t actually help them with the crime in any way. (Unless it’s help the crime happen in their jurisdiction, in which case he’s obviously guilty)