Instinct (1999)

ethan powell, once a brilliant monkey scholar, hides a secret that no one can manage to solve, not even investigators who arrested him for some murders in the rwandan jungle. imprisoned in a criminal asylum, he risks the death penalty and is entrusted to the ambitious psychiatrist theo caulder. the patient, who has not spoken for years, closes in on himself, while the doctor, willing to do anything to solve the riddle, seeks help from his daughter, lyn. thanks to caulder's tenacity, the mystery comes to the fore: the origins of powell's madness go back to the period the scholar spent with mountain gorillas who accepted it as one of them, but it won't be easy to find out what happened.