The Ape (1940 film)

The Ape is a 1940 American horror film made for Monogram Pictures, cowritten by Curt Siodmak and starring Boris Karloff.

The Ape eventually breaks into Dr. Adrians lab. The Doctor manages to kill it before any harm can come to himself. However, the spinal fluids he requires to perform his experiments have all been destroyed during the struggle between him and the Ape.Doctor Adrian then concocts an idea he will tear off the apes flesh and use its skin to disguise himself as the escaped circus animal and murder townspeople in order to extract their spinal fluid. Thus the murders will be blamed on the Ape and he, himself, will manage to avoid any suspicion. ........

Source: Wikipedia