Dd2 is a very accomlpished thief 
. She is able to steal from right under your nose and no-one notices until the offending item is found much later.
Today she has stolen a hairclip and a bath bomb from Tesco. I have taken them off her and will return them to Tesco tomorrow. She will come with me and explain why she took them to the manager.
Last week she stole a torch from school. It belonged to another little girl who was very upset when she realised it was gone. I saw the torch but she was adamant her Gran bought her it. DD1 backed her up. She returned the torch and had to draw a letter of apology to the little girl. She once stole my phone and took it to school with her. They only found out when she used it at lunch time to phone my sister who immediately rang me to let me know dd2 had my phone at school with her.
She regularly takes money from me and DH and then denies all knowledge. We never find the money. She either gives it to dd1 to take to the shop or she has a reasonable sum of money hidden somewhere.
Being caught does not seem to deter her. Nor does being shouted at or being punished. I have told her today that next time I will phone the police and they will come with sniffer dogs to search her room for stolen goods. She seems quite happy with this idea 
She is four.