(AGI) - Cape Town, Aug 26 - Johannesburg High Court Judge Thokozile Masipa today dismissed with costs South African prosecutors' application to appeal Oscar Pistorius' six-year sentence for the murder of his girlfriend Reeva Steenkamp handed down last month . "I am not pursuaded that there are reasonable prospects of success for an appeal," Judge Masipa said. Earlier, State prosecutor Gerrie Nel said Masipa minimised the seriousness of the crime Pistorius committed when sentencing him. He argued that the Masipa's decision to focus on mitigating factors when sentencing Pistorius - the fact that he was a good candidate for rehabilitation and that he showed remorse - was a misdirection of the court. Nel said Masipa should have used the minimum sentence of 15 years for murder as a starting point. Pistorius' lawyer Barry Roux hit back saying it was an insult to Masipa to insinuate that she didn't understand minimum sentences. He further argued that allowing an appeal of his client's six-year sentence would not be effective or justified. This was the State's second challenge of a ruling by Masipa In October 2014, Masipa sentenced Pistorius to five years behind bars for culpable homicide. The State challenged Masipa's finding and on December 3 last year, the Supreme Court of Appeal ruled that it agreed with the State. It overturned Masipa's verdict, replaced it with one of murder, and instructed Masipa to sentence Pistorius afresh. Pistorius shot Steenkamp four times through the locked door of the toilet in his Pretoria home on February 14, 2013. He claimed he thought there was an intruder behind the door about to emerge and harm him, and that Reeva was still in bed. (AGI) .