Witness Statement of Dr Clayton
15 October 2001 - Heard on Appeal at the Royal Courts of Justice November 2001.
I have an Honours Degree (BSc) in Biology and I am a Doctor of Philosophy (PhD) in Molecular Genetics. I hold the Common Professional Examination (CPE) in Law. I am a senior Forensic Scientist employed by the Home Office Forensic Science Services and based at Wetherby Laboratory. I have been a forensic scientist since 1990 and specialise in DNA profiling. I have participated in the research, development and validation of the STR/DNA profiling techniques currently in use by the Forensic Science Service and have been involved in the implementation of these systems for use in forensic case work, and the National DNA Criminal Intelligence Database, in England and Wales. I have conducted many examinations of the type detailed in this statement and have provided evidence for the Court of Appeal, Crown Courts, Magistrates' Courts, Coroners' Courts and for courts outside British jurisdiction. I am co-author of several scientific publications on the subject of STR DNA profiling in forensic casework and provide training to other forensic scientists in how to interpret DNA evidence.
The laboratory reference number assigned to the work recorded in this statement is D/92/1190. Further to my previous statements dated 31st August 1995 and 6th November 1995. In this statement I also refer to the statement of Dr E Meyer and Prof B Brinkman made on behalf of Bindman & Partners.
PURPOSE OF EXAMINATION
I have been asked by Mr Morris QC of Counsel to consider whether or not there is any evidence provided by the F13B locus to support the assertion that the blood on the beige paint flakes (JH2) from 24 Tandle Hill Road Royton, is of human origin (as opposed to blood from common meat products such as pig, cow, sheep).
1. Species specificity of DNA STR Typing
The STR locus F13B is found in a human Factor 13 gene which is concerned with blood coagulation. Most of the STR loci used in forensic DNA investigations are also found in the DNA of other higher primates (e.g. Gorilla, Chimpanzee) with whom we share a high degree of genetic relatedness. However no cross-reactivity is seen with the DNA of other species (porcine, ovine, bovine) or with bacteria and fungi. In the STR loci selected by the Forensic Science Service this has been demonstrated experimentally (via validation trials) and, in fact, the lack of species cross-reactivity is one of the key factor in deciding whether or not on genetic locus can be used reliably as a forensic marker. Although the F13B locus is not used by the Forensic Science Service, the Forensic Science Service has forensically validated a nearby locus known as F13A also located with the Factor XIII gene. Furthermore, I understand Prof Brinkman's laboratory have conducted forensic validation of this locus and Dr Meyer and Prof Brinkman state on pages 1 and 2 of their statement that 'A pre-requisite for the use of the STR technique is selective extraction of stains and the presence of sufficient DNA of human origin and sufficient quantity. I am also aware of research articles where the specificity of the F13B STR locus has been demonstrated practically.
2. Quality control Procedures ensuring the accuracy of DNA STR Typing
It is normal scientific practice and in accordance with accepted international standards that when testing a questioned sample, there should be included within the test batch a series of 'controls' designed to monitor the performance of the forensic typing system. This procedure was adhered to by Prof Brinkman's laboratory and observed by me. Different controls are used to monitor different aspects of the system:
1. Extraction Negative Control: This is a tube which is processed in parallel in a batch with the questioned DNA sample. It is sometimes referred to as a 'reagent blank'. This tube is exposed to all the solutions and processes as the other tubes in the batch, but does not contain a DNA sample. It should therefore produce a negative result (i.e. no typing results). It is therefore monitoring for 'general' contamination (i.e. background contamination of solutions and plasticware with DNA). It also functions as a check on sample handling.
2. Extraction Positive Control: This is a tube which is also processed in parallel in a batch with the questioned DNA sample. This tube contains DNA for which the typing results are already known. It should therefore produce a typing result which matches that previously obtained and is therefore checking that the typing process is functioning correctly. It will also serve to detect contamination if additional and unexpected results are obtained.
The results of the tests at, inter alia, the F13B STR locus, are summarised by Prof Brinkmann and Dr Meyer in a table at page 9 of their statement. In particular column 6 (headed F13B) and the rows marked III and IV contain the relevant details.
Section marked 'III Paint Flakes’
From these data it can be seen that some of the beige paint flakes from exhibit JH2 were swabbed to recover blood (ie they contained red/brown staining which had tested KM +ve). On testing at the F13B locus, a typing result of '9,10' was observed. An area of unbloodstained paint flake (marked 'JH2 - control') showed no such typing results. The same '9,10' result was also observed in the samples originating from exhibit MSN14.
Section marked 'IV Controls’
This section deals with the results from the system controls. From this it can be seen that the extraction negative (designed to detect generalised contamination) showed a series of 'weak and unspecific ladder bands' (p10 - bottom paragraph). Normally, one would expect there to be nothing present (a '*' in the notation used in the table). Dr Meyer, Prof Brinkmann and I discussed this and it was their opinion that the appearance of these bands was 'not indicative of contamination' (p10 - bottom paragraph) but that the typing results from the tests at this locus should be deemed inconclusive. We then discussed whether in view of this, the actual typing results for the F13B locus should appear in the table at all. Prof Brinkmann and Dr Meyer decided they should be listed and a 'caveat' placed in the summary that the stain typing results should be deemed inconclusive.
The results from remaining controls were as expected and did not give any indication that there was a contaminating source of DNA present in the batch used. In addition, the positive controls all produced DNA typing results in accordance with expectations.
Notwithstanding the presence of 'non-specific ladder bands' in the extraction negative control, in my opinion, the above findings taken together, show that there was a source of human (or higher primate) DNA in the sample tested from exhibit (JH2). Since a paint flake was chosen which was visibly bloodstained and given that there is no evidence of generalised contamination in the batch then, in my opinion, the most likely source of this DMA was the blood present. I have, therefore, considered two alternative propositions for the origin of the blood from the paint flakes (JH2);
1 The blood originated from a human
2 The blood originated from meat products
In my opinion, these findings taken together, strongly support the proposition that the blood on the paint flakes (JH2) was human in origin