Strange story, especially the part about "people leaving decent bikes lying around in your neighborhood," and since you want to build up a fixie, you keep your eyes open. Are they lying around in the trash bin, or on the front porch?........as for this mysterious bike from the "late" model van ("late" means newer, by the way, in this context), you know the old saying, "if it seems too good to be true, it probably is." Sounds like a stolen bike to me. Seems as though it probably does to you, too. As for what your ethical duty is, I'd say for starters stop seeking out unattended bikes that are just "lying around." Bike theft makes me mad-