South African Paralympian Oscar Pistorius is expected to walk out of prison next week after serving a year for killing his girlfriend -- but he could soon be back behind bars.

The star athlete was sentenced in October 2014 to five years in prison for culpable homicide -- a charge equivalent to manslaughter -- and is now eligible for release into house arrest after serving more than a sixth of his sentence.

Pistorius was initially due to be freed in August.

But intervention by the minister of justice led to a series of delays before the parole board announced Thursday that he would be released on October 20.

Prosecutors have filed an appeal against the culpable homicide verdict, arguing that he should have been convicted of murder over the killing of Reeva Steenkamp on Valentine's Day 2013.

If they win their case, which is due to be begin in the Supreme Court on November 3, the 28-year-old could face at least 15 years in jail.

The athlete -- known as "Blade Runner" for the prosthetic legs he wears on the track -- won international fame after racing against able-bodied competitors in the 2012 London Olympics.

His trial was broadcast live around the world.

"I think the chances are pretty good that the appeals court will rule in favour of the state and overturn the verdict," said Ulrich Roux, a criminal lawyer in Johannesburg.

"He is faced with the unusual circumstance that he's released on house arrest and then the court could find him guilty of murder and he’ll have to return to prison."

House arrest

Pistorius does not dispute that he shot his model and law graduate girlfriend four times through a locked toilet door in his Pretoria home in the early hours of February 14, 2013.

But he said he mistook Steenkamp for an intruder. Prosecutors insist that he deliberately killed her after an argument.

South African correctional services officials have indicated that Pistorius has been a good inmate and qualifies for house arrest -- a routine procedure in South Africa.

"He's not 'out' on parole... he's having his sentence converted to a house arrest sentence," said criminal lawyer David Dadic.

"He's now confined to a house for a period," said Dadic. "They'll confine him essentially to what he would be doing in prison but in the confines of his own house."

Steenkamp's parents June and Barry are outraged by Pistorius's imminent release.

"For our beautiful daughter -- for anyone's life -- it's definitely not long enough," Steenkamp's mother told You Magazine, a South African tabloid.

"She was robbed of her future, her career, her chance to get married and have a baby."

Steenkamp would have turned 32 in August this year.

A darker side

Pistorius -- whose legs were amputated below the knee when he was 11 months old -- has lost his lucrative contracts and has no immediate hope of salvaging his athletic career whatever the outcome of the appeal.

His trial exposed his darker side, offering glimpses of a dangerously volatile man with a penchant for guns, beautiful women and fast cars.

Correctional services head Zach Modise said Pistorius, who is being housed in Pretoria’s Kgosi Mampuru II prison, initially wrestled with his sentence, but then committed to reform.

"At the beginning he could not understand that you get locked up in a cell. He struggled with that," Modise told South Africa's Sunday Times.

"I think he's getting to understand you have to control your anger and temper," said Modise. "I hope when he gets released on probation he will be able to conduct himself well."

While there is speculation that Pistorius will serve his house arrest at his wealthy Uncle Arnold's house — a mansion in a posh Pretoria suburb — there is a possibility the athlete will ask to serve his sentence in a different location, away from the glare of the media.

"I think he's going to come out very quietly, and very discreetly and he’s going to disappear and stay off the radar," said Martin Hood, a criminal lawyer based in Johannesburg.

"If he breaches any of his conditions he'll lose his house arrest."

A typical offender under house arrest has his movements restricted and is not allowed to use alcohol, but conditions vary widely.

"He may have an electronic tag and he would also be subject to correctional services visits," said Hood, adding that Pistorius could have to serve community service in a hospital or morgue.