I am to trying to identify a murder mystery film, possibly from the 1970's. The setting is a large house (mansion?) near water, possibly an island. A group of people are picked off one at a time, (agatha christie style). When the murders take place, all that is shown of the killer is the hands in black leather gloves. It is revealed that the killer is a rather anemic looking, blonde girl of about 14 years of age. Thank you.