If things are as you say, then his behavior is essentially a suspension of the preparatory stage of the crime. According to the provisions of China's criminal law, voluntarily giving up the crime or effectively preventing the occurrence of criminal results in the process of committing a crime belongs to the suspension of crime. The punishment for discontinuing a crime is that the suspended crime shall be exempted from punishment if it has not caused harm, and the punishment shall be mitigated if it has caused harm.
The police station detention is affirmative, but it is to know the truth. The formal arrest is due to the fact that his subjective behavior does have the intention to commit criminal acts, or has certain social harm.