PARIS: Emile Louis, an ostensibly harmless bus driver who became one of the most notorious serial killers in French history, has died at the age of 79.

Louis, who was convicted in 2004 of killing seven mentally impaired young women in the late 1970s, died on Sunday morning in a secure hospital in Nancy in eastern France, his lawyer Alain Fraitag told AFP.

He was serving parallel life sentences for the murders and for the rape and torture of his second wife, and the sexual assault of her daughter.

His death marks the latest but not necessarily the final chapter in a tragic saga of extraordinary cruelty and judicial bungling. Exactly why it took nearly a quarter of a century for Louis to be brought to justice has yet to be explained, and mystery still surrounds the 1997 death of the police officer who first identified him as a suspect.

All seven murder victims, aged between 15 and 25, were under the care of social services in the Yonne district of northern Burgundy, for whom Louis worked as a bus driver.

Witnesses at his various trials described him as a jovial, polite man who was friendly and thoughtful in his dealings with the vulnerable young women he came into contact with through work.

But in reality, he was a sadistic predator who derived enormous pleasure from the domination of others. One psychiatrist described him as “a unique serial killer capable of inflicting extreme levels of cruelty, perversion and suffering.” Others suggested Louis suffered from a severe split personality born of the emotional abuse that he himself had suffered at the hands of his adoptive parents.

Louis first came on to the radar of French police in 1981 during an investigation into the death of Sylviane Lesage.

Investigators quickly established that Lesage had been having an illicit sexual relationship with Louis, and that he had also sexually abused three girls being looked after by his partner at the time.

Louis was convicted in 1983 of indecent assaults on minors, but a charge of murder in the Lesage case was dropped in 1984. That in turn led to the investigation into the six other murders of young women that had occurred in the area between 1975 and 1979 being shelved without anyone being charged.

Christian Jambert, a gendarme who had identified Louis as a prime suspect, was found shot dead in 1997. The death, from two bullets to the head, was officially classified as a suicide but many experts on the case suspect Jambert was murdered to cover up Louis's links to other people involved in the abuse of young women in care.

After serving his first prison sentence, Louis moved to Frejus in the south of France, where he was convicted in 1989 of sexually assaulting his neighbours' children on the camp site where he had taken up residence.

Despite the pattern of repeated sexual abuse, it was not until 2000 that Louis was finally re-arrested in connection with the seven murders. Apparently believing he could no longer be tried for them, he admitted to them in custody, only to later retract his confession.

Louis was transferred to hospital from Ensisheim prison on October 14. His death came just days before medical experts were due to issue an opinion on a request for him to be released on health grounds.