Throughout a police interrogation, the identities of police interrogators and suspects do not fix as questioners and answerers, but are dynamic with the changing communicative purposes in an interrogation process. At the opening and closing stages, the institutional identity of interrogators is salient where they act as spokespeople with suspects as recipients. At the stage of information collecting, interrogators attempt to construct an interrogation pattern where they act as recipients and suspects speakers, with an aim to show the voluntary nature of the suspect's confession. Open questions enable interrogators to give suspects the identity as narrators (of the criminal fact). However, with conflicts between different communicative purposes, the ideal pattern of interrogation is often undermined, resulting in the shifting identities of the two parties. This paper argues that the police's keen awareness of their identity construction in the interrogation will facilitate the achievement of their interrogative purposes.