Who is the actual thief?

Mr. David Howard is a Professor live in Yorkshire with his three kids and a wife, One day the family left home to attend a Wedding ceremony of his wife's Sister at Derbyshire, Unfortunately he forgot his Credit Card on his desk, but on a way to Derbyshire when they stop to buy some gifts he found out that he left the Credit Card at home When they returned back the Credit Card was gone. Now he has three suspects: the chauffeur, the tutor and the gardener, all of 'em live permanently at their home. Upon interrogating he got the answers,

The tutor said he put the Credit Card under a book on his desk to keep it safe. He checked and it is no longer there.

The chauffeur said he saw the Credit Card sticking out of the book so he put it inside again and give the book to the gardener to place it somewhere safe.

The gardener said he opens the book again witness the credit card and placed it between page 1 and 2. Again, the man checked the book and there was nothing in there...

Who actually stole it?