with one's fingers in the till;
have one's hand in the cookie jar. Stealing from one's employer. For example, He was caught with his hand in the till and was fired immediately, or They suspected she had her hand in the cookie jar but were waiting for more evidence. The noun till has been used for a money box or drawer since the 15th century; cookie jar, perhaps alluding to the “sweets” of money, dates only from about 1940.