File photo of Marilyn Monroe.

A Manhattan businessman spent US$1.5 million purchasing a tape of Marilyn Monroe performing a sex act on an unknown man and would keep it private, media reported today.

The black-and-white film is about Monroe engaging in sex with a man whose head remains out of the frame for the entire 15 minutes.

The man who bought it would not put it on the Internet and try to exploit her, according to memorabilia collector Keya Morgan who said he had arranged the silent sale recently.

J. Edgar Hoover, then FBI Director and a Kennedy rival, once brought in a few prostitutes who allegedly had been with the US President Kennedy in an effort to analyze the tape inside a lab to prove it was really Kennedy in the film.

Monroe, who was rumored to have had an affair with John F. Kennedy, died naked in her bedroom in August 1962 at age 36.

Joe DiMaggio, one of Monroe's ex-husbands, once tried to buy it from the collector for US$25,000, but was refused by the FBI informant who gave a copy of the tape to the FBI.

The informant's son, however, has sold his copy to the unnamed New York businessman.

The only other known copy is in FBI files.