The prosecutors also said they were appealing against the "shockingly light" five-year prison sentence Pistorius was given for manslaughter, as well as a third decision by Judge Thokozile Masipa to acquit the double-amputee runner of illegal possession of ammunition for bullets found in his home.
South Africa's National Prosecuting Authority said it had filed for leave to appeal those verdicts and sentence, the first step in a process that could still see Pistorius convicted of murder and sent to prison for at least 15 years for killing Steenkamp.
Prosecutors must first ask Masipa — the red-robed judge who oversaw Pistorius' murder trial — for permission to appeal against her decisions. If permitted, Pistorius' case will go to the Supreme Court of Appeal, where it would be reviewed by a panel of judges, another legal battle for the world-famous runner whose murder trial lasted seven months and left him broke, according to his defence lawyers.
Masipa acquitted Pistorius, 27, of murder for shooting Steenkamp multiple times through a toilet cubicle door on Feb. 14, 2013, and instead convicted him of a lesser charge of culpable homicide, or manslaughter.
In the appeal papers, chief prosecutor Gerrie Nel and assistant prosecutor Andrea Johnson questioned if Masipa correctly applied a section of the law called dolus eventualis when she acquitted on murder. Dolus eventualis says a person should be found guilty of murder if they realized their actions might cause someone's death and went ahead anyway, and that person died.
Pistorius shot four times through a door and into the small cubicle from close range, hitting the 29-year-old Steenkamp in the head, arm and hip.
Pistorius' claim that he mistook his girlfriend for a nighttime intruder also was not a defence against murder, the prosecution appeal said, as there was no attack on him that justified killing in self-defence.
The appeal papers were filed Tuesday at the North Gauteng High Court in the South African capital, Pretoria — the courthouse where Pistorius' trial was held. They were filed exactly two weeks after he was sentenced.
Pistorius, a multiple Paralympic champion who made history as the first amputee to run at the Olympics in 2012, is currently serving his manslaughter sentence in the hospital wing of Kgosi Mampuru II prison in Pretoria. Under the current terms, he could be released after 10 months to complete the sentence under house arrest.
"We will argue that the sentence is inappropriate and shockingly light for someone that killed an innocent person with gross negligence where his conduct bordered on dolus eventualis," the prosecution said in its appeal against the sentence.
Prosecutors also said they'd appeal the acquittal on an illegal possession of ammunition charge after Pistorius didn't have a license for bullets found in his home, but testified they belonged to his father.
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