While this doesn't help you now, in the future, just have your developer use source control. Github is a popular tool for this. Let's you pay and own the account, they just check in code as they go. Lets you have control and see the progress they are making.
Keep in mind that contractors get screwed by clients; often. The only leverage you have sometimes is the source code. If you really are the good guy here (you paid in full) then hopefully you can work it out.
If the contractor really is shady; is it possible you tried to save a buck and went with the cheapest and least reputable person?