Dino Maglio, who was a police officer in Padua, was jailed for six and a half years after being found guilty of drugging and raping the girl at the end of a fast-track trial late on Tuesday, Ansa reported.
The attack happened in March 2014 when the girl stayed at Maglio’s flat in Padua with her mother and younger sister.
Prosecutors said the girl, who had stayed up chatting to Maglio after her mother and sister had gone to bed, was given a drink spiked with tranquilisers of a type which have featured regularly in date-rape cases.
When the mother woke in the morning, she discovered her daughter in Maglio's bed without her underwear and in a state of extreme lethargy.
Arrested after the family filed charges in Venice, Maglio admitted having spiked the girl's drink and to having sexual intercourse with her while she was under the influence, but claimed the sex had been consensual.
The 35-year-old is still being investigated for either carrying out or attempting similar assaults on up to 15 other women, who he also allegedly lured through the website.