A former Stanford University swimmer convicted of sexually assaulting an unconscious woman outside a fraternity house has been released from prison after serving half of a six-month sentence that critics condemned as too lenient.

In the latest twist to a case that has ignited controversy across the USA, Brock Turner walked out of Santa Clara County jail in California at around 6am yesterday and climbed into a white SUV after spending just three months behind bars. The 21-year-old told authorities he plans to live with his parents in his native Ohio, where he must register as a sex offender for life.

The case dominated the news amid allegations that the judge had imposed a lenient sentence because of Turner’s status as a student at an elite university. The judge had sentenced him to six months, despite a powerful written statement delivered by his victim in which which she outlined the impact the attack had on her.

“Every day, I have to relearn that I am not fragile; I am capable; I am wholesome; I am not just the livid victim,” she wrote, addressing Turner directly.

“Your life is not over. You have decades of years ahead to rewrite your story. But right now, you do not get to shrug your shoulders and be confused anymore. You have been convicted of violating me intentionally, forcibly, sexually, with malicious intent.”

The controversy prompted California politicians to pass a tougher sexual assault law and led to an effort to remove the judge involved in the case from the bench.

Turner was convicted of assaulting the young woman near a rubbish bin after they drank heavily at a party in January 2015 at the university located near San Francisco. He has said he plans to appeal his conviction.

The judge will no longer hear criminal cases following the controversy (AP)

During a sentencing hearing in June, Santa Clara County Judge Aaron Persky cited the “extraordinary circumstances” of Turner's youth, clean criminal record and other considerations. He said he had followed the probation department's recommendation for a moderate jail sentence.

Following backlash and a push for a recall, Mr Persky voluntarily removed himself from hearing criminal cases, something that is to start next week.

The Associated Press said that Greene County Sheriff Gene Fischer said Turner had five days to register as a sex offender with his office in Xenia, Ohio, 15 miles east of Dayton. He will have to report to a probation officer for three years and must avoid alcohol and drugs during that time.

Mr Fischer said his department will send postcards to Turner’s neighbours informing them that a convicted sex offender is moving in nearby. Turner will be required to register every three months in person at the sheriff's office, reaffirming that he is still living with his parents, the sheriff said.

Loading....

Police officers will also check on Turner periodically and without warning to ensure he has not moved out without permission from authorities, the AP said. Turner also is barred from parks, schools and other places where children are expected to gather.

“He will be treated no differently than any other sex offender we monitor,” said Mr Fischer.

Turner was apprehended by two Stanford students, who testified that they intervened because the woman appeared to be unconscious. As they approached, Turner fled. The two men gave chase, apprehending Turner and restraining him until police arrived to take him in custody.

In her letter, the woman described blacking out at a party and waking up in a hospital with pine needles in her hair, dried blood and bandages on the backs of her hands and elbows, her underwear missing.