[from occupied ga]

Be able to document that you never touched an 80% receiver that was machined at your shop. A simple way to do this would be to require that participants wear red gloves, and you wear no gloves, then video the machine operations showing the hands doing the operation

This is logically impossible. You cannot prove that you didn't do something.

[marktwain]

The prosection has to prove that you did something.

You do not have to prove that you did not. You only have to provide the jury with reason to doubt a lie.