Multisig bitcoin ownership didnt exist at the time this happened. Its more akin to the teller cleaning out the cash from the bank because the manager asked him to do something he didnt like then burning the money when told to give it back. Its a question of ethics.
Of course If I have too I will pay the coins back myself however there is no way for me to know who owns them without access to the db. As nefario said this is closed untill the parties sort it out.
Multisig has nothing to do with this. The coins are the property of witcoin. The information to access those coins should have been protected and secured. Witcoin (you) failed to do this, and now are liable.
If he used this access information to drain the account, it would clearly be theft. However, having simple knowledge of how to access the coins was part of his duties, and is not incriminating in any way.
You should consider yourself lucky, and be grateful that misery can restore this information to you. I don't understand why you are threatening him.