STOCKHOLM (AFP) - A Swedish man long considered Scandinavia's most notorious serial killer was released on Wednesday from more than 20 years of psychiatric detention, eight months after being cleared of all charges.

"The court rules that the forensic psychiatric care of Sture Bergwall shall continue and change from closed to open care," the administrative court in Falun said in a statement.

Sture Bergwall, 64 - previously known as Thomas Quick - confessed to dozens of murders in the early 1990s and was convicted to life imprisonment for eight of them and held at a psychiatric ward in Saeter in northern Sweden since 1991.

He was later cleared of all the murders due to lack of evidence, amid revelations that he had been heavily medicated at the time of the confessions.

The court ruling which ordered his release added that he still suffers from a "personality disorder" but not to the extent that he should be held in custody.

Several conditions were placed on his release, including that he avoid alcohol and drugs, undergoes regular treatment and accepts help from local authorities in his new home.

Bergwall has blogged and tweeted regularly in recent years and has said he planned to move further north to live in the mountains and devote himself to writing about his experience.

"Those acquittals show there was a legal scandal... it was not my mental health that formed the basis of my detention, it was the judges' and the clinic's reputations," he wrote on Wednesday.

"I have a lot to tell and that is what I will spend my time on now... I look to the future with great confidence." The convictions against Bergwall have been dubbed Sweden's greatest miscarriage of justice in recent times because of the swiftness with which he was found guilty of the eight murders, which occurred between 1976 and 1988.

During psychological counselling, following an armed robbery conviction, he confessed to all eight murders as well as more than 20 others in Sweden, Norway and Finland for which he was not tried.

He often described how he butchered his victims and how in at least one case he ate body parts.

In December 2008, however, he suddenly retracted all his confessions, saying he had been craving attention at the time and had been heavily medicated by doctors.

In July 2013 he was acquitted of the last murder charge.

A number of high-ranking opposition politicians and legal experts have called for an independent commission to examine how Swedish courts could have convicted Bergwall despite the lack of evidence.

Justice Minister Beatrice Ask announced a review in July 2013.