Peter Cropp, a former ESR scientist, said in evidence on Thursday he believed blood staining on one of the socks was more likely to have been caused by droplets of blood falling on the sock from above, rather than from the wearer stepping on blood.
But although his initial evidence was he believed the blood spots had been airborne, Dr Cropp agreed with defence counsel Helen Cull QC that if tests had been done showing the staining could have come from blood being walked on, rather than dropping from above, he could not exclude that possibility.
Dr Cropp, was the fourth of a group of forensic science experts the Crown is calling in 37-year-old David Cullen Bain's second trial for the 1994 murders of his parents and three siblings.
The hearing, before Justice Graham Panckhurst and a jury of seven women and five men, goes into its fifth week in the High Court at Christchurch on Monday.
Bain is represented by Michael Reed QC, Ms Cull, Paul Morton and Matthew Karam, while Kieran Raftery, Cameron Mander and Robin Bates are prosecuting for the Crown.
The Court has heard evidence about the amount of blood found throughout the house, particularly in 14-year-old Stephen's bedroom where he was killed after a violent struggle.
And witnesses have described bloody sock prints from a right foot which were revealed by luminol testing.
Some of the prints were partial, some complete and were located in Margaret Bain's bedroom which adjoined Stephen's room, in the hallway, and one moving in and one moving away from Laniet's bedroom.
Dr Cropp said he had grouped the blood from the sock, and found it could have come only from Stephen or Laniet.
Laniet and Stephen were shot dead in the family's Every St home along with their older sister, Arawa and parents Robin and Margaret Bain, on June 20, 1994.
David Bain was later charged with the murders although the defence say it was not David but Robin who shot the family and then himself.
The Crown says the blood on the socks showed David Bain, not his father, was the killer.
For the particular blood mark to have been made on the sock from the wearer walking in blood, it would have to have been a relatively fresh blood stain with no signs of drying, Dr Cropp said.
He had not carried out any experiments himself to establish whether the mark could have been made in the way Ms Cull suggested.
But he would accept, if experiments had shown it, that the staining might have occurred as Ms Cull was suggesting.
Because both socks were in the same bag and not labelled as to whether they were left or right, he was unsure which foot the sock in question had been on.
But if it had been worn in the normal manner, the spots would have been somewhere on the bottom and edge of the sock.
Dr Cropp also told the court about examining a blood splattered green curtain from the front of a computer alcove beside where Robin Bain's body was lying.
During his first examination of the curtain in 1994, he found nine elongated spots of what appeared to be blood.
He tested one and found it was blood and could have come only from Robin Bain.
He was asked to examine the curtain again in 1997 to see if he could establish what position the blood had come from.
He told Crown counsel Cameron Mander the tests he did in the ESR laboratory in Auckland indicated the blood had come from an area less than one metre above the floor and close to the curtain.
The tests indicated the stains all intersected between 600mm and 750mm above the bottom edge of the curtain which was itself less than 250mm above the floor.
And the blood had come from a source that was, horizontally, less than 120mm away from the surface of the curtain.
The Crown says Robin Bain was kneeling next to the curtains when he was shot by a person, they say David Bain, who was hiding behind the curtain in the alcove.
Dr Cropp said he also found a spot of human blood on the other curtain but it was too small to group.
He also gave evidence of testing blood from several door jambs in the house.
A sample of blood from a door jamb to the pantry was confirmed as human blood and could have come from David, Stephen or Laniet, but not Arawa or the parents.
Testing of another sample from a blood spot in the hand basin in the bathroom showed that could have come from the same three siblings.
To Ms Cull in cross-examination, Dr Cropp agreed the blood may have arrived on the curtain as Robin Bain was falling from a standing position.
But he said the measurements he had made should not be taken as indicating the position of Robin Bain's head when the bullet entered.
It took time for blood from head wounds to flow freely.
Asked whether the shape of the blood marks could indicate that they were arterial blood, Dr Cropp said it was possible, but there was usually a "wave" type of pattern with arterial blood, indicating the pumping motion.
He said he had not been handed a 10-shot magazine which was on its edge on the floor near Robin Bain's body although he had seen the note made by fellow ESR scientist Peter Hentschel.
It was clear Mr Hentschel had intended the magazine to come to him for testing.
And he had not been asked to look at any samples from Robin Bain's hands nor was he aware a blood smear had been noted on the heel of one of the hands.
He could not recall Mr Hentschel talking to him about scrapings or blood from under Robin Bain's finger nails.
He had never received such samples.
He agreed with Ms Cull that, in his position as a blood analyst specialist, he could have analysed a blood smear "if there was sufficient material in the blood".
Asked by Ms Cull about the gel plates from the original blood tests going missing, Dr Cropp said he was "shocked" when he heard the plates had gone.
To Mr Mander in re-examination, he said while the originals of the blood sample tests had been destroyed, a photocopied record had been retained.
Those copies also showed the dried-down gels used in the testing although the colours of the various "bands" could not be seen, just their position.
And he said the two sports socks had been checked by a podiatrist who said the second sock appeared to have the characteristics of a right foot because of the curvature of the stain that was shown with luminol.
Next week, the court is likely to hear evidence from the four other forensic scientists and from pathologists.
