My previous employer Stop Payment'd my last check for multiple reasons, what can I do?

I got a letter in the mail today from a lawyer saying my paycheck is being held due to multiple reasons..

"He informs me that you were terminated from your employement on July 1st. Thereafter, without the consent or knowledge of **** you accessed the restaurants computer files. You also deleted/stole the operations manual both on paper and the computer version and a list of drink recipes. None of these items belong to you. While you may have helped in the formatting the manual, you don't own it. The manual and the recipes are owned by ***. You also accessed the restaunts FB page and deleted information without the consent of ***"

First, when I was hired I did not sign a confidentiality agreement nor a non-compete agreement. I also signed nothing stating that anything I create for this business is then their property.

Secondly, they have no proof that I took anything off the property (I actually didn't remove anything from the restaurant).

Third, the drink recipes are recipes I created years ago at a different job. Can they stake claim to them if I have proof that I made them prior to my employment there?

He's threatening to not only hold my pay but report unauthorized computer access to the police. Every employee has access to the computer he's speaking of... What can I do?