Database & File Security Audit

Please only bid if you have experience with security audits. I recently had a freelancer here who did some minor work on a WHMCS module that is about 10 files. I have a reason to believe he may have installed some back door to our database, or inserted something to the database because he was claiming he could delete all the data in our database if he wanted to after we changed all passwords. This happened after being away for a week and he thought I disappeared so he made threats while I was away. I am looking for someone to audit the database and the module files to find if he added anything that would allow him access still or anything else that seems suspicious.