Your first step is to contact an experienced intellectual property attorney that can help you determine the best course of action and guide an investigation. You have several options for dealing with the employee. All but one could create difficulties in the future.

A written warning, probationary period, and repayment all sound like appropriate disciplinary measures until you think about the impact on the rest of your employees. Not only will these remedies send a message that the theft was not serious, but you are also allowing someone who stole from you once to have the opportunity to do so again.

Termination, as harsh as it sounds, is your only real choice for employee theft. To build the case for termination you need to:

Gather evidence. Video and digital evidence are strong. A witness is also appropriate.
Audit the computer files and financial records.
Preserve documents, computer files, and emails.
Maintain a chain of custody to prove there was no tampering with the evidence.
If you perform interviews or any other investigation, document everything you learn. You will need it when you report the theft to the police and to make an insurance claim to recover losses.

Your attorney can help you with civil liability even if the theft is not prosecuted as well as assist in the termination process, especially if the employee is a union member or part of a collective bargaining agreement.

As an entrepreneur or small business owner, learning that an employee has stolen from your company can feel like a threat to your child. Take measured steps to gather evidence to prove the wrong-doing on the advice of your attorney. To prevent future issues, put a policy and basic accounting controls in place.