I is absolutely illegal, both civilly and criminally in the State of Illinois for your emp... to withold an employees paycheck. If an employee embezzled 1,000,000,000. Employer is still at fault.
He has no right to withold your check, and you will be entitled to attorney's fees, interest on the judgment, and all costs if you are required sue your employer in a court of law. Even if you still have the lap-top.
It is wrong for you to keep his lap top of course, but you have not stolen it, and there is no reaon for him not give you your check. What happens to you if you don't get your final pay check? Compare that with his business not having the laptop, which he knows he will have if he simply pays you your check.
Your employer is absolutely in the wrong, but I can't condone you illegally witholding their property (though it is not a crime), however, I understand your situation. Good luck.