UPSC Civil Services 2025 Prelims General Studies Paper II

A mobile phone has been stolen. There are 3 suspects P,Q and R. They were questioned knowing that only one of them is guilty. Their responses are as follows:
P : I did not steal. Q stole it.
Q : R did not steal. I did not steal.
R : I did not steal. I do not know who did it.
Who stole the mobile phone?