Rento

You are a psychologist, who is appointed to speak to a mentally ill man that was involved in a crime revolving on a killer that is on the loose, and their only clue is this guy as you remember the detectives telling you, he had seen the killer but wouldn't say a thing beside, "He, he, he, he.." As if he was traumatized too such a degree of insanity. The detective also warned you to not try to force him to anything, since he tried to kill an officer. He also warned to gain his trust cause for some reason he would panic to the point he'll knock them out if he knows they are just using him. The next day, it'll start, and you should be ready. Will you be able? Or will this crime remained unsolved?