Does an individual bear sin for concealing thefts that occur before him at work?

A Muslim must change evil with their hand; if unable, then with their tongue; if unable, then with their heart. This is because failing to condemn evil when one has the ability to do so is considered participation in the sin. Therefore, you should first advise those committing the evil. If they do not respond, then you must inform whoever is able to stop them, such as the owner of the stolen money, even if you do not reveal your identity. It is preferable to provide documents that prove the veracity of your statement to clear your conscience and avoid sin.