Fingerprints in blood were found on the rifle that killed the Bain family. There was no doubt that these were David Bain's prints.  There were no signs of Robin Bain's prints on the gun.

The Defence disputed the presence of human blood and argued that the prints were from a hunting trip several months prior and may have been rabbit blood or not blood at all.  This assertion goes against the findings of the investigation done in 1994 while the fingerprints were fresh, and were determined to be in blood.  Sure, in 2009, 15 years later it is probably impossible to determine what the fingerprints are formed from, but that doesn't mean that the original conclusion is not valid.  In addition to this, the activity on the morning of the killings with and without the white gloves on would have removed or damaged any old prints and certainly put them into the background.  

The Defence produced expert witnesses who state that often fingerprints are not left on murder weapons after they have been used, but in the David Bain case there were fingerprints on the murder weapon, so this situation simply does not apply here.  In addition to David's fingerprints on the butt there were prints on the silencer belonging to Stephen that are consistent with him trying to fend off an attack.  Were these left from a previous hunting trip too?  In the case of the fingerprints, Karam has really sought to pull the wool down over the eyes of the jury.

We can accept the expert testimony that it is possible for a person to use a rifle and leave no fingerprints, however in the Bain case there were fingerprints so it simply doesn't apply.  No expert got up to testify that it is possible for someone to shoot 4 people including having a life and death struggle with one of them and all the while leave old fingerprints intact.  One expert for the Prosecution said words to that effect but in general this gaping hole in the Defence argument wasn't seen by the jury.

The defence can't have it both ways:
1.  A person can leave no fingerprints on a rifle after using it
2.  A person can use a rifle to shoot 4 people and leave previous fingerprints fully intact

The original examination in 1994

Kim Jones, a fingerprint technician with the Christchurch police, said he examined the rifle on 21 June 1994 and discovered "sharp, definitive and recent'' fingerprints belonging to David Bain. The fingerprints were deposited by fingers covered in blood which when tested returned characteristics consistent with human blood.

Earlier he said after a visual examination of the rifle on June 21, 1994, he had put the rifle under an intense light called a polilight that enhanced fingerprint images and found that "the rifle was covered in its entirety - itself, the stock, the strap, the scope and the silencer, '' with blood.

Fingerprints in blood were located on the right hand side of the fore-end of the stock as though someone had put a hand over the top of the rifle's stock from above.  These matched David Bain's fingerprints from four fingers of his left hand, Jones said. The prints had been placed by fingers covered in blood on a clear surface and were "sharp and very definitive''.  The fingerprints had been placed with such pressure and were so clear he was left in no doubt they were of recent origin. Over time fingerprints degraded but these were very clear, he said.

The defense argued the actual bloodied fingerprints were never sampled and were old fingerprints deposited by David with rabbit blood on his fingers.  Kim Jones the police fingerprint technician said if prints were put on the rifle during a hunting trip before the murders, they would have been destroyed with subsequent handling.  He said he believed the prints were recent because the hemoglobin in the blood had not oxidized and the blood had therefore not turned dark brown in color.  Such prints would have “dramatically destroyed or smudged’’ during the activity on the morning of the murders, he said.

Another scientist, Dr Cropp, said he was given five plastic tubes with blood samples scraped from the rifle.  His testing confirmed the five samples were human blood and four of them were of one particular type. The blood could have come from David, Stephen or Laniet, but not from the rest of the family. There was a huge amount of blood in Stephen's room. The killers gloves were literally dripping with blood, without doubt there would have been plenty of blood deposited on the rifle.

The 2009 Retrial

The Defence called in British fingerprint expert Carl Lloyd as a witness and he claimed that the fingerprints were not in human blood and may not in fact be in blood at all.  He was no doubt aided in this by the fact that by now the prints were 15 years old and had deteriorated so much that nobody could be certain of their composition sufficiently to be able to successfully contest these claims.

The Defence also claimed that it is possible for a killer to leave no prints on a rifle after using it.  This claim, while true, stems from the fact that often the gun is wiped down to remove fingerprints after it is used.  If either David or Robin had done this on this particular occasion then David's fingerprints would not have been so clearly evident on the rifle and if Robin had done the shooting then his fingerprints would be on the rifle.  There was no sign whatsoever of any of Robin's prints on the rifle.

Conclusion

The fingerprints on the gun are undisputably David's and are in human blood therefore they connect David closely to the crime.  The Defence argument about animal blood on the gun is weak because the activity on the morning of the murders would have destroyed them, and also, when shooting small animals, only negligent amounts of blood are ever transferred to the hands, if at all, when picking them up (that is if they are picked up and not just left lying in the field). The gun, as described was covered in blood.

More in depth reading on this subject can be found here and here

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