[susan53]

I'm not completely sure what you mean here. It doesn't "refer to" anything. Was your question really "What does it mean?" ? If so, it means to adopt an attitude of potential suspicion or doubt towards something (in our case, the suspect). In other words that they were not necessarily going to believe what they said.

As I said - the verb to question automatically involves this type of attitude. Even if the police are questioning a witness, or even a victim, they have to allow for the possibility that the person is mistaken (witnesses aren't always reliable) or even lying. Just saying : The police questioned the suspect/witness/victim about XXX inevitably suggests that they were open to the possibility that what they heard was not true.