David Bain's sister Laniet told a doctor it was going to be difficult for her to abstain from sex at a time she was going to stay with her father, the Bain murder trial has heard.

Dr Marjolein Copeland told the High Court at Christchurch today that she met with Laniet Bain, 18, at her Dunedin medical practice for the first time in November, 1993. From her medical notes, she recalled Laniet was "on guard" and "business-like", and was carrying a large cellphone.

Dr Copeland said Laniet stated she was a prostitute and complained of pelvic pain. She said she told Laniet she would need to undergo tests for a Sexually Transmitted Disease (STD).

As she was about to do the tests, Dr Copeland said Laniet answered a call on her cellphone and told the caller that she would be unavailable for four days because she going to be staying with her father out at Taieri Mouth, south of Dunedin.

Dr Copeland said she did the tests, and told Laniet it was highly likely she had an STD. She advised her to abstain from sexual activity for four days and prescribed her antibiotics.

At this point, Laniet's demeanour changed and she became anxious and fidgety. She said Laniet told her: "That's not going to be easy".

Dr Copeland said she told Laniet that she had overheard her cellphone conversation about going to stay with her father.

Laniet did not appear happy with this, and left the surgery quite quickly, Dr Copeland said.

David Bain, 37, is on trial for the murder of his parents and three siblings in their Dunedin home on June 20, 1994. His defence team say Robin Bain, 58, shot dead the family before turning the rifle on himself.

The defence say Laniet had been involved in an incestuous relationship with Robin Bain, and Robin was fearful of word of this getting out.

Dr Copeland said she saw Laniet again briefly in December, 1993, when she came in without an appointment seeking contraceptives.

David Bain's fingerprints

The High Court also heard from a fingerprint expert who supported the defence theory that David Bain's fingerprints got on the rifle used to kill his family months before the murders.

English fingerprint consultant Carl Lloyd, formerly of Scotland Yard, has told the Bain High Court murder retrial he disagrees with the views of the police fingerprint officer who found the prints on the .22 rifle that was used to shoot dead five members of the Bain family on June 20, 1994.

Police fingerprint officer Kim Jones has stated that David Bain's fingerprints were found in blood on the wooden stock of the rifle and were of "recent origin" because of the extensive pressure applied.

The pressure applied meant Bain could not have simply picked up the rifle to have a look at it, Mr Jones said.

Mr Lloyd told the court today there was not doubt the fingerprints belonged to Bain. But he said there was nothing to suggest the fingers had been placed in blood on the rifle stock, or with excessive pressure.

Excess pressure invariably led to fingerprints being blanked out because the ridges and furrows in the prints were brought together. The prints could simply be left by picking the rifle up.

Mr Lloyd said he was of the view that the prints left by Bain were not in blood, but could be in sweat or contaminated by some other substance such as gun oil.

Bain's defence say the prints could have been left on the rifle when Bain went hunting a few months before the shootings of his family.

Prosecutor Kieran Raftery put to Mr Lloyd that the defence case had previously been that Bain's fingerprints had been placed on the rifle in animal blood, to which Mr Lloyd repeated there was no blood in the fingerprints.

Mr Jones has stated that if these prints were left months before the murders, they would have dried out and become "flaky", and subsequent handling of the rifle would have destroyed them. Mr Lloyd disagreed with this.

Once left to dry, fingerprints could stay in place on an item for years if undisturbed. Mr Lloyd knew of one murder case in Britain where a fingerprint had lasted seven years.

Prints in blood had been known to last two or three years after being created.

"Fingerprints can last a considerable amount of time. It depends where you leave it."

Mr Jones also held the view that if the fingerprints had already been on the rifle, they would have been "dramatically destroyed or certainly smudged" when the killer carrying the rifle was involved in a violent struggle with Bain's brother Stephen, 14.

Mr Lloyd said the area of the rifle where the prints were may not have been disturbed. The prints would have to be wet to be smudged and "in fighting presumably that area was never going to be used".

Asked about a fingerprint belonging to Stephen that was found on the silencer of the rifle, Mr Lloyd said there was no way of knowing when it was left in relation to Bain's prints.

Mr Jones has also given evidence of Bain's palm print being found in blood on the washing machine in the family home.

The prosecution said this print was made when Bain washed his bloodied clothing after shooting his family but Mr Lloyd said today it was unclear when this print was left on the machine and that it was not necessarily left in blood.

Asked by the jury whether there would be genetic similarities in the fingerprints of Bain and his father Robin, Mr Lloyd said there might be loose similarities.

Bain, 37, is on trial for the murder of his parents and three siblings in their Dunedin home, but his defence team say Robin Bain, 58, shot dead the family before turning the rifle on himself.

There has been no evidence of fingerprints belonging to Robin being found on the rifle.

Robin Bain's wound

The trial earlier heard that it was inconceivable that Robin Bain was seated when he suffered a fatal gunshot wound.

English forensic scientist John Manlove described patterns of blood staining going in different directions on Robin's pants when he was shot in the left temple.

This was consistent with a method of suicide in which Robin had bent his right knee and raised his leg onto a chair. Blood had impacted both above and below the knee, creating the different directions.

This method of suicide has been demonstrated to the court by English firearms expert Philip Boyce, using the rifle which was found next to Robin's body and killed five members of the Bain family.

The prosecution have put to Dr Manlove that the same blood patterns could be caused on Robin's pants with him seated and his knees bent when he was shot.

Asked today by Bain's lawyer Helen Cull QC about this prosecution theory, Dr Manlove said he found it "inconceivable".

Taking into account the height and distribution of blood around the lounge where Robin was found, the facts were "entirely not in keeping with that proposition".