Getting legal advice is not a bad idea. However, generally, you have every right to track the employee's work conduct as it relates to the embezzlement. For example, you could install business software to track where the funds are going, etc. You could have the police open a case, and perhaps they will advise to set-up their own surveillance. There are many details left out of your question, such as why you believe there has been theft, the documents supporting same, etc. I wish you the best.