The Old Man Who Cried Wolf(1970)

Emile Pulska is visiting his old friend Abe Stillman. During the visit they are attacked and Emile is struck senseless. When he wakes up he is told that Abe is dead, dead by natural causes, the doctors tell him. When Emile insists that they were attacked, his relatives try to give him psychiatric help. Emile decides to try to find the killers himself, but someone is watching his every step...