We're told it was started deliberately.
Girls 'Tied Up By Two People'
A forensic scientist has told a court it is "likely'' that two teenage girls killed 37 years ago were tied up by different people.
The High Court in Livingston heard the bindings used on Christine Eadie "showed different knot-tying characteristics'' to those used on Helen Scott.
Witness Roger Ide said the findings indicate the victims had been tied by two different people - although he explained it did not represent strong evidence to that effect.
The evidence emerged on the sixth day of the trial of Angus Sinclair, 69.
He denies raping and murdering the 17-year-olds, who were last seen at Edinburgh's World's End pub on October 15 1977.
Sinclair is accused of carrying out the attacks along with his brother-in-law Gordon Hamilton, who is now dead.
Mr Ide, 72, now retired, told the court of his experience in analysing knots during his career as a forensic scientist.
The court heard how he prepared a report for the court in May this year after being asked to look at various ligatures used to bind the two girls.
His report, which he read out to the jury, concluded: "The bindings to Christine Eadie showed different knot-tying characteristics to those used to secure Helen Scott.
"This indicates that the two victims had been tied by two different people, but it does not provide strong evidence to this effect.''
During his evidence, the court heard how two reef knots - said to be a more uncommon form of knot - were found on the bindings on Christine's body.
Mr Ide said it appeared that she was tied by someone who knew more about what they were doing.
He told the court: "I've looked at many bindings to victims of different sorts over many years and you sort of recognise the handwriting, almost.
"I can't be certain but it looks to me as if Christine Eadie was tied by someone that knew a little bit more about what he was doing than Helen Scott.
"None of the knots used to secure Helen Scott were skilful at all.
"Two of the knots on Christine Eadie were the same, a more skilful knot.''
He went on: "Someone may have thought it out a bit, known a bit about what he was doing.''
Discussing the conclusion of the report, he stressed that his findings should not be overstated.
"My concern is that everybody watches CSI programmes and they see forensic scientists provide conclusive evidence,'' he said.
"I don't want to overstate the strength of my evidence... But I think it's likely that the two were tied by different people, but I can't be sure about that.''
In Christine's case, the witness also described how her wrists were bound in a way similar to when handcuffs are used.
"It indicates that she wasn't willing to be tied,'' Mr Ide told the court.
Jurors have previously heard that Christine's body was found at around 2.25pm on October 16 1977 at Gosford Bay, Aberlady, and Helen's body was discovered at around 6pm that day in a field near Haddington in East Lothian.
Sinclair denies the charges against him and has submitted three special defences of incrimination - blaming his brother-in-law, now dead; alibi - saying he was fishing on the banks of the Firth of Forth near Cockenzie power station at the time; and consent to sexual intercourse.
William Burns posed as a postman.
Police and other emergency services were called to a property in Redburn, Bonhill, Alexandria, at about 12.30am on Tuesday.
Charities say the stage it's diagnosed is crucial.
Most Viewed Pictures On Heart
Recently Played Tracks
To listen live, choose your preferred station:
Now playing: The best feel good music
Deposit £10 to get a £40 Welcome Bonus - That's £50 to play bingo, slots and more!*
Over 50 tracks to make you feel-good. New album out now...
Find your local four day weather report here.
Find out more about some of the companies advertising on Heart Scotland- East.