Carnival of Blood (1970)

A brutal murder has taken place at Coney Island amusement park, and DA Dan is assigned to investigate and bring the killer to justice. For some reason, he decides to celebrate his engagement to Laura by inviting his fiancee to come with him and enjoy the park, even though there is still a violent murderer running loose. As the body count rises, Dan must sift through the clues before he or Laura become the next victims.