Open access. Looking in from the outside, what would the ordinary person expect of forensic mental health services? I suggest that there are three questions he or she would ask: (a) Are there public health measures that can be introduced to prevent those with mental disorder going on to commit crimes? (b) Can we identify in advance the individual who is likely to go on and commit a violent act because of his or her mental health difficulties, and prevent that or limit damage? (c) If a seriously harmful act has already been committed, what interventions might prevent a repetition? All of these questions are about prevention of an untoward event in the future and anticipate knowledge. How secure can we be that current forensic mental health practitioners can make adequately evidenced responses?...........