The State had proved beyond reasonable doubt that "Sunday rapist" Johannes Jacobus Steyn murdered and kidnapped teenager Louise de Waal, Judge Sita Kolbe said on Tuesday.
In handing down judgment in the High Court sitting in Alberton, Kolbe said: "The State proved beyond reasonable doubt he kidnapped and murdered her."
Steyn was aquitted on a charge of raping De Waal.
Steyn pleaded not guilty to two counts of murder, 11 of rape, 10 of sexual assault, 10 of kidnapping, one of attempted sexual assault, and one of attempted kidnapping.
The murder charges relate to the deaths of Louise and another schoolgirl Lazanne Farmer.
He allegedly abducted De Waal in October last year while she was on her way to school in Roodepoort. It was just before her 17th birthday.
De Waal's burnt body was found on a Magaliesberg farm later the same day.
Steyn handed himself over at the Margate police station in KwaZulu-Natal the next day.
Farmer, 14, from Pretoria was kidnapped in September 2010 by a man in a bakkie.
She died after jumping out of the bakkie in a bid to escape.
Last week, the State contended that Steyn premeditated his killings, and used a fire enhancer when he set De Waal alight. Prosecutor Mutuwa Nengovhela asked the court to take into consideration that most of De Waal's burns were on her thighs, suggesting that Steyn tried to destroy evidence.
Two alibi witnesses denied Steyn's claims that they were with him on the days some of the crimes were committed. - Sapa