World's End killer Angus Sinclair is believed to have killed at least six other people.

Sinclair, 69, was said by a judge to be worse than evil after he was convicted yesterday of the 1977 rape and murder of teenagers Helen Scott and Christine Eadie, seven years after being cleared of the crimes.

But the psychopath, already convicted of two other homicides in 1961 and 1978, was also named as the chief suspect in the killings of five women and one man in the 1970s.

The potential toll of 10 would make him modern Scotland's most prolific serial killer.

The 69-year-old's conviction brings to a conclusion one of the country's most infamous unsolved cases and marks the first prosecution since changes to Scotland's double jeopardy law.

The legal change meant Sinclair, who has been in jail since the 1980s, could be retried after the court case against him dramatically collapsed seven years ago.

At the High Court in Livingston, judge Lord Matthews said the words "evil" and "monster" were inadequate to describe Sinclair, who he said had left the bodies of the 17-year-old girls "to rot like carrion".

The judge ordered him to spend a minimum of 37 years in jail for the crimes. It is the same number of years that the families of Ms Eadie and Ms Scott have been waiting for justice and the longest term of any prisoner in Scotland.

Sinclair, an inmate at Glenochil jail in Clackmannanshire, showed no emotion when the jury returned its verdict last night following the five-week trial.

He had claimed the girls consented to sex with him and accused Gordon Hamilton, his brother-in-law and accomplice, who died in 1996, of killing them. However, DNA analysis proved Sinclair had touched the ligatures used to tie the girls up.

Yesterday Lord Matthews told him: "Little were they to know that they had the misfortune to be in the company of two men for whom the words evil and monster seem inadequate."

Forensic scientists described how about 125 stains on the pieces of clothing used to restrain the girls had been examined during at least two years of meticulous testing.

In 2001 another DNA breakthrough had seen Sinclair convicted of the 1978 murder of Mary Gallacher in Glasgow.

He had been jailed in 1961 for the murder of a seven-year-old neighbour, Catherine Reehill, when he was just 16.

But retired Detective Chief Inspector Allan Jones, 52, believes Sinclair is responsible for 10 killings, six of them unsolved, and that he would travel around the country claiming victims like the Yorkshire Ripper.

Mr Jones said Sinclair had a unique "modus operandi".

In a joint inquiry by Lothian and Borders and Strathclyde Police, Sinclair was identified as the chief suspect in the World's End murders as well as the rapes and murders of Anna Kenny, 22, in August, Hilda McAuley, 36, in October and Agnes Cooney, 23, in November of the same year.

Ms Kenny, Ms Cooney and Ms McAuley all disappeared in Glasgow. They were all bound and gagged in the same way.

One of the FBI's leading criminal profilers said another woman, Frances Barker, 37, had met a similar fate after going missing close to Sinclair's Glasgow home, although another man, now dead, was convicted of that crime.

Mr Jones also believes Sinclair killed Eddie Cotogno, 63, an amateur pornographer and friend of Sinclair, in Glasgow in 1978, and Helen Kane, 25, whose body was found on a hill overlooking Holyrood Park in Edinburgh in 1970.

His killings ended before 1982, when he was jailed for life for rapes.