Assessments made by the original ESR scientist were of the opinion that the finger impressions on the gun were in human blood.
From the PCA Report (section 276). Note that references to trial are for the original trial in 1995.
Mr Hentschel gave evidence at the trial of obtaining five samples of blood from the rifle to pass on to Dr Cropp for analysis. He stated that " ... blood was taken from the silencer, from the front of the telescopic sight, from the barrel, from the stock near the trivger and also from the fore arm from where those fingerprints were found...". Dr Cropp, ESR, then gave evidence at the trial "that the five samples were all identified as human blood." The blood on the rifle [silencer, barrel, and wood near the trigger] was able to be grouped to Stephen's, Laniet's or David's.
These initial tests were later reviewed (section 277):
As part of the Review, Dr Harbison examined the case notes of Mr Hentschel and Dr Cropp and conducted a series of tests. Mr Hentschel conducted a chemical test (Sangur) on areas of probable blood staining on the rifle the results of which were positive (ie. indicates the presence of blood.) Those samples were further analysed by Dr Cropp who conducted an ouchterlony test, which is a test that detects the presence of a human protein. These tests on the samples, and in particular, the area around the fingerprint, were also positive.? Dr t1arbison's opinion was that the original two tests conducted by Mr Hentschel from blood being wiped across its surface. Mr Hentschel gave evidence at the trial that ", .. smears of blood were found over most parts of the rifle" ... and "blood being wiped across the surface.,. Senior Fingerprint Officer Jones said in his statement to the review team that" ... it was almost like it [rifle] had been wiped down with something soaked in blood ... " but he also agreed that it could be just covered in blood because someone in the course of a fight has been covered in blood and contaminated the gun.
Since these initial tests were done the samples have been sitting around for over a decade. During that time the composition of the blood samples has deteriorated somewhat, making it difficult to ascertain their true nature, therefore tests done in the lead up to the retrial in 2009 can easily produce negative results. In light of that, an expert contracted to examine the samples after 2000 may not be able to determine whether or not the blood is human and therefore, under cross examination in court is able to state, that from his examination of the blood, it could belong to any mammal. Other experts might not even be able to determine if the samples are blood at all, and since oil is also made of organic compounds, are able to testify that, according to their examination of the evidence, the samples may not even be blood but may be oil or grease. In light of this, the earlier tests on the fingerprints should be given higher significance and the later ones seen in the light of the deteriorating evidence.
In regard to the bloodied fingerprints, the question has to be asked with respect to the argument that the blood on the gun was from a previous hunting expedition: How were these prints still preserved after all the activity on the night of the murders, including the life and death struggle with Stephen? The Defence got an expert witness to testify that the blood could have been animal blood from a previous hunting expedition and another to testify that a person can use a rifle and not leave any fingerprints but they did not produce an expert witness to testify that you could carry out an energetic mass murder, not leave your fingerprints but leave fingerprints from a previous hunting expedition.