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?

To solve this logic puzzle, we must evaluate each suspect as the potential thief while considering that the question does not specify how many suspects are telling the truth or lying.

If P is the thief: P lied about himself and Q. Q told the truth about R and himself. R told the truth about himself and his lack of knowledge. This scenario is logically possible.

If Q is the thief: P told the truth about himself and Q. Q lied about himself but told the truth about R. R told the truth about himself and his lack of knowledge. This scenario is also logically possible.

If R is the thief: P lied about Q but told the truth about himself. Q lied about R but told the truth about himself. R lied about himself. This scenario is also logically possible.

The problem does not provide a rule regarding the number of truth tellers or liars. Without a constraint such as only one person tells the truth or two people are lying, we cannot pinpoint a single guilty person. Therefore, the identity of the thief cannot be concluded.