Our country’s law clearly stipulates that the maximum period of detention is 37 days, but in reality many cases exceed this period. Therefore, this time we can only communicate with the public security organs and the procuratorate to inquire about the situation.
As for writing letters, you can indeed write them, but it is not certain whether you will receive them. No one can say for sure what the circumstances of the detention will be. As for lawyers, lawyers can intervene in the case after the suspect has been questioned for the first time. However, the rights of lawyers are not guaranteed and evidence is difficult to obtain. It depends on the lawyer's ability.