Tell the thief that he is now your slave
From Create Your Own Story
You smile and tell him that his brother will be taken care of under one condition. "And what's that?" He asked afraid. You tell him that you'll protect his brother if he becomes your slave. He look at you considering his options. You remind him that if he refuses than you'll turn him into the Royal Guard and he wouldn't be able to help his brother. He sighs and says. "You leave me no choice. I'll be your slave."
You smile and take him in magic shackles to the castle. You take him to your room and connect the chains on his arms to the roof and then create chains spreading out his legs connecting to the floor. You take a step back to admire your handy work. Now that you have a thief chained up in your house what do you do?