Former Stanford swimmer Brock Turner files an appeal to overturn conviction so he doesn't have to register as a sex offender

Brock Turner, the former Stanford swimmer convicted of sexually assaulting an unconscious woman. Photo / AP

A former Stanford swimmer convicted of sexually assaulting an unconscious woman outside a campus fraternity party is appealing.

In an appeal filed Friday, lawyers for Brock Turner said the initial trial was "a detailed and lengthy set of lies".

They hope a new trial will also help overturn his mandatory lifetime requirement to register as a sex offender, reports Daily Mail.

The case gained national attention when Judge Aaron Persky sentenced Turner to six months in jail - he served just three.

NBC Bay Area reported that John Tompkins, Turner's legal adviser, said what happened was not a crime.

Tompkins said the facts do not reflect the verdict, which is why they are appealing.

Turner was never convicted of rape but was instead found guilty of three counts of felony sexual assault.

He was arrested after being seen penetrating a drunk, unconscious girl with his fingers behind a dumpster on Stanford's University Campus in California in January 2015.

The star swimmer was initially indicted with two counts of rape, two counts of felony sexual assault and one count of attempted rape. He denied all of them.

The rape charges were dropped during his trial but he was convicted of three counts of felony sexual assault in March 2016.

He could have been jailed for up to 14 years, the maximum sentence in California, but instead was given just six months imprisonment and three years probation. Turner served just three of those months before being released last fall.

He has been registered as a sex offender and has to report to a probation officer for three years, during which he is not allowed to drink or take drugs.

During the trial he admitted to being drunk at the time of the incident and said he'd dabbled with LSD.

The sentence sparked outrage and was considered by many as proof of the justice system's unfair treatment of rape victims and abysmal handling of sexual assault cases.

As part of the trial, Turner's victim, a 23-year-old who was not a student at Stanford but who was visiting, described the horrors of the legal system and how it had tortured her since the case was brought to light.

Turner's father fueled public fury when, in a letter to a judge begging him to spare his son jail, he described it as "a steep price to pay for 20 minutes of action".

"His life will never be the one that he dreamed about and worked so hard to achieve," Dan. A. Turner wrote.

Turner became the face of the college campus sex scandal which engulfed the US in 2016 and which continues to be fought over and challenged by activists across the country.

The judge who sentenced him was investigated for misconduct but was cleared and has defended his decision ever since he delivered it.

Santa Clara County Judge Aaron Persky said it was his duty to give first time offenders lenient sentences.