I work for a commercial enterprise owned by a Muslim. One day, I saw a fellow Muslim worker stealing some goods. Should I tell the owner though I have no witnesses other than myself?

All perfect praise be to Allaah, The Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and messenger.

Any Muslim who sees the property of another Muslim being stolen or damaged has to save it, especially if he has been entrusted with it. Therefore, you should have prevented this person from stealing and reminded him about Allaah and the Day of Resurrection. 

However, given that the goods have already been stolen, we advise you to advice this person either to bring goods similar to those he had stolen or pay their price or ask for the pardon of the owner. If he refuses, you should tell the owner about the stolen goods so that he may demand his rights.   

The fact that you have no witnesses should not stop you from telling the owner unless it is most likely that the owner would believe the thief and consider you a liar.