Alleged overpayment of wages by employer/denial of three paychecks

My employer did not pay me for three recent pay periods, alleging he had overpaid me in the past. I provided him all information proving he had not overpaid me and requested paychecks. He did not pay me so I terminated my job and made a wage complaint with the State. When I quit he told me he had "movies" of me on my computer showing I had once looked at matresses online while I was working and that he had the neighbors watching me and that I had come to work late and did not work the hours I claimed. He never had specific requirements for time, I set my own hours and always worked all hours that I billed. He has threatened to try and charge me with theft. He reviews all paychecks and hours and personally signs them and never questioned any of my hours during the two years I worked for him. Currently he owes me $4,000 in wages. He told me he thinks he overpaid me $20,000, he had not provided any evidence of this claim and threatened me saying I would never work in this town again if I don't repay him or work for him for free. What would be my next best step?