Convicted murderer Oscar Pistorius only needs to serve three years before he can apply for parole.

A leading criminal law expert believes Paralympic star Oscar Pistorius could serve only half of his six-year murder sentence.

An emotionless Pistorius, 29, was sentenced in the North Gauteng High Court yesterday for shooting dead his girlfriend Reeva Steenkamp in 2013.

Lawyer William Booth says if the Blade Runner behaves himself behind bars, he could be out as early as 2019.

Judge Thokozile Masipa said she believed there was strong enough evidence “to deviate from the prescribed sentence of 15 years”.

She says: “Each case is different. This court is indebted to both counsel, referring to previous cases with similar precedents. However, none of those cases have the exact same circumstances as this case.”

Masipa, quoting from other court cases regarding public opinion, said: “A sentencing policy that catered predominantly to public opinion was inherently flawed.”

She said the views of ordinary mense not involved directly in Pistorius murder case should be kept out of court.

“Public opinion may have some relevance, but cannot replace the court’s duty.”

In weighing up testimony for and against Pistorius, Masipha concluded: “I am of the view that the mitigating circumstances outweigh the aggravating factors.”

Pistorius will not be appealing his sentence.

Andrew Fawcett, an instructing attorney in the defence team, said: “We respect the decision made by Masipa and we won’t be lodging any applications for leave to appeal going forward. Oscar will serve his sentence as handed down by Judge Masipa.

But legal eagle Booth says: “His lawyers can make applications to the parole board in three years’ time and with support from correctional services to confirm his good behaviour he could be released.”

The lawyer also believes that it was the right decision for Pistorius to not appeal his sentence.

“In my opinion, it’s a lenient sentence with the minimum sentence for murder being 15 years.”

“If you go on appeal there is the possibility that the Supreme Court of Appeal could increase the sentence, especially because it’s nine years less than the minimum for murder.”

Booth says he thinks Judge Masipa “made too much of Oscar’s remorse”.

He says: “Remorse is a mitigating factor but in this case I believe it should mean more than going to the victim’s family and saying you’re sorry.

“Remorse would be an admission of guilt on at the very least culpable homicide.”

Reeva’s family preferred not to show the media any reaction to the sentencing.

Dup de Bruyn, lawyer for Barry and June Steenkamp, told reporters shortly after the sentence: “They only wanted the law to run its course, and that has happened. They abide by the ruling.

“They will, from now on, have a dignified silence. We cannot change anything.

Asked whether the Steenkamps were disappointed at the six-year jail term, De Bruyn declined to comment.

He, however, said he had strongly advised the family not to appeal the sentence.

“We cannot decide for the prosecution. As I’ve explained to the family, it is not so easy to go on appeal with a sentence,” he said.

Even if the family doesn’t agree with the six years [jail term], they cannot just interfere with it.

“For the family to interfere, it must be a shockingly disappropriate sentence and they say we could have imposed this or that.

“But we are not entitled to interfere with the decision of the judge imposing sentence.”

Mobbed by reporters shortly after Judge Masipa handed down sentence, the Steenkamps declined to directly speak to the media.

Pistorius’ sister Aimee was in tears outside the court as she waited for her brother to be transported back to Kgosi Mampuru Prison.