BROOKSVILLE — The Hernando County Sheriff on Thursday identified a man he said raped a 12-year-old girl and threatened her sister and friend while they were home alone in 1983.Detectives believe William Louis Nichols, then 42, broke into the house in Ridge Manor with a knife, grabbed a 9-year-old girl and said he'd kill her if the 12-year-old, her sister, didn't cooperate. A 10-year-old girl was there, too.Nichols took the eldest girl to a bedroom and raped her, Sheriff Al Nienhuis said. Nichols died in Orlando in 1998, authorities said.After the April 1983 incident, the girls told detectives that a white man between 30 and 50 years old committed the crime."One thing the 12-year-old did say ... was that the suspect was unusually calm in the way he committed this brutal crime," the sheriff said.Detectives collected DNA samples from the scene, but had no matches with them until recently, when Sheriff's Det. George Loydgren worked with two DNA labs.Detectives gave one company their evidence, and the company handed back a list of likely physical traits that matched the girls' description.The company performed a genealogy analysis and told detectives Nichols was the only likely suspect.Detectives got DNA from a family member. It matched samples from the 1983 scene, Nienhuis said.Investigators found Nichols' name connected to several rape cases from his home state, Wisconsin. In 1958, he was convicted of attempted rape, released on parole in 1961 and taken off probation in 1964.He was charged with rape eight years later, but was found incompetent for trial and institutionalized. Later that year, he was arrested on rape charges that were dismissed.At the time of the Ridge Manor case, Nichols ran a vending machine service business and traveled around central Florida, officials said."We believe (the DNA), coupled with his proximity to the crime, and of course his criminal history, I think we can comfortably say ... Detective Loydgren solved this case," Nienhuis said.Loydgren visited the victim on New Year's Eve to tell her the news."Immediately, her jaw dropped," he said."The 12-year-old little girl inside that grown woman still has to deal with the impact of this horrific crime on her life," Nienhuis said.The sheriff believes it's likely Nichols committed other rapes, and his agency has sent details to other law enforcement departments.Contact Justin Trombly at [email protected] or . Follow @JustinTrombly.