There was no reasonable doubt that "Sunday Rapist" Johannes Jacobus Steyn murdered and kidnapped teenager Louise de Waal, the High Court sitting in Alberton found on Tuesday.
Handing down judgment, Judge Sita Kolbe said: "The State proved beyond reasonable doubt he kidnapped and murdered her."
Steyn was acquitted on a charge of raping De Waal.
Kolbe said Steyn was a "self-confessed liar" who admitted to lying to his wife and his boss.
The judge said it was improbable that a mechanic at his workplace had disabled the tracking system in his bakkie, which helped him because his vehicle could then not be tracked.
She also said it was unlikely that an unknown person placed De Waal's bag in the bin in Steyn's yard.
He was in the vicinity of where the murder took place. His two cellphones placed him there via cellphone towers tracking activity on his phone.
As a result, the only inference that could be made was, "that it was the accused who abducted Louise and subsequently killed her".
Steyn was also found guilty of culpable homicide for the death of teenager Lazanne Farmer.
"There was testimony that no medical assistance could have saved her," said Kolbe.
Farmer's sister started crying in court when the judgment was handed down.
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.