Answer
To take the patient into your clinical room, offer him a seat, explain who you are, and assure him that you are there to help him and could best do this if he would talk to you — this would be most appropriate action.
There may be one of several reasons why he remained mute. For example he may be very frightened, aware that he might be attacked by other inmates; or deaf; or totally uncomprehending that he had done wrong, or indeed in a catatonic stupor.
The doctor would need to spend some time with such a patient, away from prison officers and in a non-threatening environment in order to undertake an assessment.
If you have any doubts then it would be best to admit him to the prison health care centre for the night under the observation of nursing staff, and reassess the situation the following day.