He was detained for three months, which shows that the compulsory measure taken now is arrest. There may be criminal detention before arrest.
The handling of criminal cases needs to go through three stages: investigation, prosecution and trial; Public security (or procuratorate), procuratorate and court are respectively responsible. Compulsory measures to restrict personal freedom can be taken in these three stages, and the time limit does not overlap. In other words, in the public security, detention has been a month. At the procuratorate, the detention period was recalculated.
So detention for three months does not mean that the case has been decided. It is suggested to ask the host police officer about the progress of the case now.