A forensic scientist's ­conclusions in the case of a man accused of murdering two teenage girls 37 years ago are "misguided, unjustified and positively misleading", a court has heard.

Angus Sinclair, 69, denies raping and murdering Christine Eadie and Helen Scott, both 17, who were last seen at the World's End pub in Edinburgh on October 15, 1977.

He is accused of carrying out the attacks along with his brother-in-law Gordon Hamilton, who is now dead.

The High Court in Livingston has heard six days of evidence from forensic scientist Geraldine Davidson, who works with the England-based company Cellmark. Ms Davidson talked the jury through DNA samples taken from items of clothing that were used as ligatures to bind and strangle the girls.

She told the court analysis of one of these - the belt from Helen's raincoat that was found around her wrists - suggested the two girls may have still been together when the ligature was tied.

But defence QC Ian Duguid said forensic scientists had prepared a report for the defence that did not agree with this conclusion.

He said: "You are making a conclusion which is misguided, unjustified and positively misleading." Ms Davidson replied: "I appreciate that's their interpretation of these findings. I don't agree, and stand by my interpretation of the findings."

The jury has heard a defence report detailing Mr Sinclair's version of events, in which he claims he and Hamilton had consensual sex with both girls in a vehicle in Holyrood Park, after which Mr Sinclair left to go fishing.

He claims the girls were "alive and unharmed" when he left their company, and he has lodged three special defences of consent, alibi and incrimination.

Mr Duguid said: "There are three different circumstances to consider. One of them is that some consensual sexual activity had taken place between Mr Sinclair and both of the girls.

"Two, that Mr Sinclair wasn't there when the girls were killed, and three, he is blaming a named individual Gordon Hamilton for the killing of the two girls."

Ms Davidson's report concluded that Sinclair had been in contact with "most if not all" of the ligatures in the case.

Mr Duguid suggested Mr Hamilton could have been the person who transferred Sinclair's DNA on to the pieces of clothing used as ligatures.

He said: "Leaving aside the belt section of Christine Eadie's ligature, am I right that every single one of the samples taken across the ligatures had Gordon Hamilton as either the major or most prominent contributor?"

The witness replied: "Largely speaking, yes."

She added: "We know they had been together. The potential for one to transfer the other person's DNA is a viable option."

Mr Duguid continued: "So every single site could have been Gordon Hamilton transferring Angus Sinclair's DNA by a secondary transfer?"

"It could have, yes," she replied.

Mr Duguid also questioned the robustness of some of the results in Ms Davidson's report, suggesting the jury had been "bombarded" with results, some of which were of "doubtful reliability".

Ms Davidson said she hoped she had made clear to jurors the limitations of some results when taking them through the evidence.

Ms Davidson told the court there was rarely a definite yes or no answer with forensic science.

She said: "It's not just if ­something is possible, it may be possible but that doesn't mean it's probable."

The trial, before judge Lord Matthews, continues tomorrow.