Most of the older police files are destroyed, the more recent ones (maybe 1950's on) exist but you won't get access to those of course.
However small parts of the police files may be found with the archived court files at the BANQ, assuming of course the file was selected for archiving at the BANQ. There are several courts' indexes which need to be used to find the files.
The prison registers are kept in a BANQ offsite storage facility and they have to be ordered to the BANQ main site in advance. It can take several weeks or months. They are yearly ledger books and can be accessed up to year 1919. These registers are for the Bordeaux prison. I don't think other prison registers exist). Right now the BANQ is closed.