Luminol testing of the carpet in parts of the house where five of the family were shot dead on June 20, 1994, revealed partial and complete right footprints, the complete prints being measured at 280mm by forensic scientist Peter Hentschel.
The Crown says David Bain, the sole survivor of the multiple homicide, made the prints as he moved through the house killing the family.
But the defence say the prints were made by David's father Robin, that Robin Bain shot his wife, two daughters and younger son before shooting himself.
The court has heard that Robin Bain's foot was measured in the mortuary and was 270mm in length.
David Bain's foot is just over 300mm (30cm).
Mr Hentschel said in evidence he would expect the foot that left the 280mm print to be longer than the print itself.
But defence counsel Michael Reed QC challenged him on that point, saying evidence from another ESR scientist being called by the Crown and from an overseas expert the defence was calling would contradict Mr Hentschel's theory.
Mr Reed also suggested Mr Hentschel was not being fair and straight forward in his evidence as was required of an expert witness.
He asked if yesterday was the first time during the past 15 years that Mr Hentschel had mentioned in evidence that he would expect the foot making the 280mm print to be larger than 280mm.
Mr Hentschel agreed it was the first time.
He is the first of the Crown's eight forensic scientist witnesses whose evidence will be heard during the next few days in the retrial of 37-year-old David Cullen Bain for the murder of his family.
Bain, who won a retrial after Privy Council hearing in 2007, served 12 years of a 16-year non-parole life term for the five murders on which he was convicted in 1995.
He denies the five charges.
The trial, before Justice Graham Panckhurst and a jury of seven women and five men is now into its fourth week of hearing and is expected to last until some time in mid to late May.
Mr Reed asked Mr Hentschel what tests he had done to establish whether a foot would be larger or smaller when walking.
Mr Hentschel said that, before the 1995 trial, he had carried out tests using fingerprint ink on the sole of socks while he stood on a piece of paper and had measured the resulting print.
The print was smaller than the length of his foot, but he agreed that had been done to show the difference between prints left by a shoe and by a foot.
It was never done as a careful test, walking on carpet.
Mr Hentschel said he was aware ESR scientist Kevan Walsh had done a test using blood-soaked socks walking on carpet and he agreed his test with finger print ink on socks and standing on a piece of paper was not the same level of testing as that done by Mr Walsh.
He believed the last time he was asked about the size of the luminol prints would have been about 2000, although he could not be sure, but he said he had always felt the foot that made the 280mm print, as revealed by the luminol and measured, was larger than the print itself.
He agreed the print he had made was not the basis of a scientific opinion.
He accepted he had not undertaken testing like Mr Walsh, using blood-soaked socks walking on carpet.
Asked whether, when he observed blood on a carpet from a walking foot, the print would be slightly larger than the actual foot due to pressure and "a bit of slippage", Mr Hentschel said he did not know.
"I would have to test that."
And he did not know whether the print would be slightly larger when it was treated with luminol.
Asked whether he thought it fair to venture an opinion when he had not checked the ESR's tests, Mr Hentschel said from his experience, it was his view the length of the print shown by the luminol was less than the length of the foot that made it.
"I suggest that's fallacious, that the foot can't be bigger. It can only be smaller. That's what the tests will show," Mr Reed said.
"If they do show that, what do you say?" he asked Mr Hentschel.
"If they show that, I would be wrong," the witness replied.
After a series of further questions on the same topic, Mr Hentschel said he had to accept Mr Walsh had carried out some tests, and if the answers to the findings Mr Walsh had given as relayed by Mr Reed were correct, it would appear a foot grew when it deposited blood on a carpet and was luminoled.
But he said he found that "strange".
"I believe a foot that makes a print has to be larger than the print it leaves behind."
Whether a walking foot would make a larger print than a standing foot would depend on how a person walked.
There would be areas of the foot that would not make contact with the surface underneath.
Mr Reed then asked Mr Hentschel about David Bain's socks and the fact both socks had blood on them.
The witness agreed both socks had blood on the soles, but only prints from a right foot were found.
Asked about why the pieces of carpet with the prints had not been cut and kept for further testing, Mr Hentschel agreed they could have been retained and sprayed again with luminol.
He said he had only once in his 40 years as a forensic scientist gone back and re-tested a crime scene with luminol.
An expert from the UK would give evidence it was possible that the carpet could have been sprayed again with luminol, even a year later, Mr Reed said, to which Mr Hentschel replied "If certain procedures are followed, I guess it's possible to spray again".
But the information obtained the next time would not be as good as with the first spray and the pattern would start diffusing because a water solution was involved.
Earlier in his evidence, Mr Hentschel told the court he had tested skin samples taken from Robin Bain's hands and found no particles he could say were gunshot residue particles.
He also tested swabs from David Bain and found no gunshot residue particles.
Under cross-examination, he agreed the tests on the skin samples were not carried out until September and October, 1994.
He also found dirt and "some possible blood" in fingernail scrapings taken from Robin Bain's hands, but nothing else.
There was not enough of what might have been blood for any further testing, he said.
Mr Hentschel was challenged by Mr Reed about his evidence concerning blood on the knee of Mr Bain's blue track pants.
He said he believed the blood dropped from a height when Mr Bain was standing.
But Mr Reed said one of the United Kingdom's most experienced blood splatter experts would give evidence saying Mr Hentschel was wrong.
The witness said it was "not impossible" he could be wrong, that an opinion was "just an opinion".
He said he had no scientific basis for his opinion on the direction of the blood other than that the blood spots were not joined together.
