I don’t believe this was part of the Inner Sanctum series, but it may have been part of something similar or perhaps it was a stand alone film.
A man has invited a group of former friends and others to his house. I recall the man was wealthy.
The man was originally left for dead, by these friends years earlier, but he was saved by a mystic who taught him mysticism to the man save his life. The mystic has stayed with him ever since as an employee and assistant.
The mystic demonstrates his abilities to these people by going into a trance and causing a skeleton to materialize in their midst from an ancient tomb.
The murders begin shortly after this. The man is accused, but he shows them that he has no arms or legs.
Each time before the killer strikes the insects grow silent outside in the night and the odd walk of the killer is heard. Additionally there is a lot of blood left by this killer at the scenes of the murders and odd footprints. In the end it is discovered that they mystic taught the man well, as he was able to materialize skeletal legs and arms onto his body to carry out his crimes of revenge.