Olympian Oscar Pistorius was convicted of murder Thursday in the 2013 death of his girlfriend, Reeva Steenkamp, The Associated Press reports.

Pistorius, 29, was found guilty by a South African appeals court, which overturned a prior conviction of manslaughter. He faces a minimum of 15 years in prison under South African law, but may be sentenced to less time due to the fact that he is disabled and is a first-time offender. The sentence will be handed down at a later date.

Steenkamp was fatally shot by Pistorius on Valentine's Day morning in 2013. The athlete claims he believed Steenkamp was an intruder, but prosecutors said the shooting took place after an argument between the couple.

Pistorius, a double amputee who was nicknamed Blade Runner because of his carbon-fiber prosthetics, has been under house arrest since October, when he was released after serving one year of a five-year sentence stemming from the manslaughter conviction. He was not in the courtroom when the new verdict was read.