Someone else being convinced it is wrong doesn't make so either.

Seeing as how it seems to be a gray area I am willing to let the person taking the frame determine if they are playing the role of thief or not since the owner does not seem to be around.

When they locked I am sure they wanted to keep it.

As much time has past and many parts have been taken off the bike and it has still been neglected by the original owner and time still continues to pass with no sign of care from the original owner it becomes less clear if the owner has just abandoned the bike or not. I can see how someone could easily to the conclusion its abandoned OR still owned by the original owner depending on your perspective.