Can any psychiatrist serve as a forensic psychiatrist? Or do they have to have a special certification?

Forensic Psychiatry. There is a psychiatric specialty called forensic psychiatry, and there are postgraduate training and board certification, and also a grandfathering association which grants board certification based on the work and credentials of the psychiatrist applying to it. The most important is the experience of the professional in the field of forensics.
Although Forensic. Psychiatry is a board certification (with some grandfathered in) - many psychiatrists testify in court as expert witnesses that are not formally trained in a forensic fellowship.