I'm not sure " putting the letter in the file" is good enough, in the unlikely event that they come back at you for non-compliance. In my experience deadbeats who already know that their deductions exceed the balance aren't concerned about being found.
I darn sure would be careful about contacting them at work, particularly the " getting them fired" part. That's a very clear vioation of the Fair Credit Collection Act, which is one of the few federal consumer protection laws that anyone takes seriously.
Forget about suing, and (the correct word is not garnish) but GARNISHEE, 99.9% of all small claims judgements in the US are against people who are " judgement proof" .
One of the things that I always did was mail the INSPECTION REPORT within a day or so of move-out, without the check! That keeps them from cashing the check and then coming after you. Of course in this case there wouldn't be a check!
all cash