South African state prosecutors have filed an affidavit to oppose Oscar Pistorius’ bid to overturn his murder conviction with the constitutional court. The National Prosecuting Authority said Monday the appeal arguments are “without merit and contrived” and the South African Paralympian, who was sentenced to five years in prison for the 2013 killing of his girlfriend, has “no reasonable prospect of success,” according to local news broadcaster eNCA.

State prosecutors further said it was in the interests of justice that Pistorius be sentenced “on the crime he has committed.” The 29-year-old athlete, who was granted bail in December and has been living under house arrest, is scheduled to return to the High Court in Pretoria on April 18 for sentence proceedings, eNCA reported.

Pistorius was charged with the premeditated murder of his girlfriend, South African model Reeva Steenkamp, who was found shot to death in February 2013. The double-amputee Olympic sprinter, nicknamed the "Blade Runner" for his metal running blades, admitted he did fire the shots that killed Steenkamp through a bathroom door but said he thought he was firing at a home invader. But prosecutors argued that Pistorius shot Steenkamp during an argument.

In October 2014, Pistorius was sentenced to five years in prison for culpable homicide — South Africa’s equivalent to manslaughter — and also given a suspended three-year sentence for an unrelated firearms charge. But South Africa’s Supreme Court of Appeal on Dec. 3 overturned the ruling, finding Pistorius guilty of killing Steenkamp. Pistorius is facing a minimum of 15 years in prison.

After spending a year behind bars, Pistorius has remained under house arrest at his uncle’s home in a suburb of Pretoria. Earlier this month, the athlete applied to appeal to the constitutional court in a final effort to overturn his murder conviction, which has seen him barred from returning to the track until 2019.