How do I help my friends business?

My friend has entrusted someone to look after his restaurant and build up the business , but now he is rude to the staff and he thinks he owns the place. Recently he has bought a �10k watch and a �10k car. And when recently the accountant found out the books don't tally up. Now my friend feels hurt by this. He is now looking at ways to find out if he is taking money from the business.