Ring

Two teenagers, Masami (Hitomi SatÅ) and Tomoko (YÅ«ko Takeuchi), talk about a videotape recorded by a boy in Izu which is fabled to bear a curse that kills the viewer seven days after watching. Tomoko reveals that a week ago, she and three of her friends watched a weird tape and received a call after watching. Tomoko is killed by an unseen force as Masami watches, horrified.
Days later, Reiko Asakawa (Nanako Matsushima), a reporter investigating the popularity of the video curse, discovers that her niece Tomoko, and her three other friends, mysteriously died at the same time, on the same night, with their faces twisted in fear. She also discovers that Masami became insane and is in a mental hospital. After stumbling upon Tomoko's photos from the past week, Reiko finds that the four teenagers stayed in a rental cabin in Izu.
Reiko goes to Izu and arrives at the rented cabin, where she finds an unlabeled tape in the reception room of the teenagers' rental cottage. Watching the tape, Reiko sees a series of seemingly unrelated disturbing images. As soon as the tape is over, Reiko sees a mysterious reflection in the television and receives a phone call, with an unknown voice telling her "seven days". Disturbed, she leaves the cabin.
Reiko enlists the help of her ex-husband, RyÅ«ji Takayama (Hiroyuki Sanada). They take a picture of Reiko and find her face blurred in the photograph. RyÅ«ji then watches the tape, against Reiko's objections. A day later, Reiko creates a copy for RyÅ«ji for them to study. They find a hidden message embedded within the tape saying "frolic in brine, goblins be thine". The message is in a form of dialect from Izu Åshima Island. That night, Reiko catches her young son Yoichi watching the videotape; claiming that Tomoko had told him to do it. Reiko and RyÅ«ji sail for Åshima and discover the history of the great psychic Shizuko Yamamura, who was accused of faking supernatural powers; and thus committed suicide.
With only a day left, Reiko and RyÅ«ji discover that the videotape was made psionically by Shizuko's lost daughter, Sadako Yamamura, whose supernatural powers surpassed even those of her mother. The two go back to Izu with the assumption that Sadako is dead and her vengeful spirit (OnryÅ) killed the teenagers. They uncover a well underneath the cabin and through a vision see the circumstances of Sadako's murder by her father. They try to find Sadako's body in an attempt to appease her spirit. Minutes before her seven days are up, Reiko finds Sadako's corpse, and they believe that the curse is broken.
The next day RyÅ«ji is at home and his TV switches on by itself, showing the image of a well. The ghost of Sadako crawls out of the well, out of RyÅ«ji's TV set, and frightens him into a state of shock, killing him via cardiac arrest. Before dying, he manages to dial Reiko's number; she hears his last minutes over the phone and realizes the videotape's curse remains unbroken. Desperate to save her son, Reiko realizes that copying the tape and showing it to someone else saved her. With a VCR and RyÅ«ji's copy of the tape, Reiko travels with her son to see her father in an attempt to save him, realizing that this is a never-ending cycle: The tape must always be copied and passed on to ensure the survival of the viewers.

Question: Who murdered Sadako?
Answer: Her father; Her father