Dr Balding & the CSI effect
Dealing with mathematicians is like your three wishes in a fairy story. You get three questions and they answer them literally. So you ask could LCN DNA be present after a knife was washed. Problem 1) this is really chemistry so Balding ceases to be an expert opinion. 2) Literally he is right. Within the limits of the question DNA could be left on a knife after washing (unless bleach was used).
The question one really wants to ask is in the case of a knife allegedly used in a bloody murder which does not match most of the wounds or the imprint left behind, that was not collected or stored in recommended ways for LCN samples, with no detectable blood, even in crevices which would be hard to clean. What is the likelihood that a LCN DNA profile from a swab from the blade with no detectable DNA, tested in a laboratory which is not set up to do LCN DNA, with no information about negative controls, can be safely attributed with reasonable certainty as deriving from the use of the knife in the murder.
I am a bit surprised that Balding seems unaware of the issues of the 'in machine' data processing and the need to ensure the data output is reliable. Lots of people believe an instrument output; they are happy with it being a black box. Modern instruments do a lot of processing, an example is the 'bug' that reports on the RTqPCR a value of 50 for no detectable DNA. Literally this implies that DNA was detected after 50 cycles. In fact no DNA is detected. The software needs a numerical value so defaults to 50. It is entirely reasonable to expect to have the 'raw' data prior to in machine processing because the settings may filter out small but significant signals.
Balding: "Sollecito is fully represented in the stain at 15 loci (we still only use 10 in the UK, so 15 is a lot),
the evidence against him is strong even allowing for the additional uncertainty due to non-replication."
CH: [
Are there contributors to the Y-STR profile other than Raffaele Sollecito? If so, how does the presence of this DNA affect our interpretation of the bra clasp as evidence?]
BALDING: "
I haven't looked closely at the Y evidence - there seems no need for it because the autosomal evidence is overwhelming for the presence of DNA from Sollecito. But from a look at Conti-Vecchiotti, it seems to back up the conclusion from the autosomal profiles: Sollecito's alleles are all represented and these generate the highest peaks, but there are some low peaks not attributable to him;
so at least one of the additional contributors of low-level DNA to the sample was male."
Are there contributors to the Y-STR profile other than Raffaele Sollecito? If so, how does the presence of this DNA affect our interpretation of the bra clasp as evidence?
I haven't looked closely at the Y evidence - there seems no need for it because the autosomal evidence is overwhelming for the presence of DNA from Sollecito. But from a look at Conti-Vecchiotti, it seems to back up the conclusion from the autosomal profiles: Sollecito's alleles are all represented and these generate the highest peaks, but there are some low peaks not attributable to him; so at least one of the additional contributors of low-level DNA to the sample was male.
CH: The bra clasp was collected about 47 days after the murder, and it was found in a different location from where it was initially observed. In the interim many people entered the cottage and items from her room were removed. Are these concerns sufficient for the clasp to be excluded as
evidence?
BALDING: The only worry would be if somehow DNA from Sollecito was brought into the room and deposited on item 165B. I don't know enough about what happened to say if that was likely but I'd guess that people walking in and out of the room etc would be unlikely to do that.
CH: The clasp was collected with gloves that were not clean, not with disposable tweezers (videos here and here). The glove was handled by more than one person. Are these concerns sufficient for the clasp to be excluded as evidence? If not, should the clasp be given less weight as evidence because of them?
BALDING: Same comment - the only concern is if any of this could have transferred DNA from Sollecito onto item 165B.
CH: Would you care to comment on the storage of the clasp after the forensic police tested it?
I know nothing about it.
CH: Did you analyze the electronic data files? Did you examine the laboratory¹s own protocols and machine logs?
BALDING: I have only seen the epgs for the autosomal DNA profiles of 165B. There is an unclear version of them in the Conti-Vecchiotti report, but Prof Vecchiotti kindly provided my with a clean set.
CH: Did you examine the negative controls?
BALDING: No.
I'm not an expert on the science issues, but I have to say I'm concerned by Balding's phrasing at several points in this interview.
He seems to have two areas of pre-concieved prejudice that I'm troubled by:
1. He thinks that Sollecito is a suspect - ok, fine. But he equates a finding of Raf's DNA by saying,
"the evidence against him is strong". It doesn't sound like he's talking about the certainty of a match to Raf's DNA, but rather he is chaining the idea of a finding of Raf's DNA to "
evidence against" Raf.
It's as though he is suffering form the "CSI" effect, that the presence of DNA is automatically incriminating, and since Raf is the suspect, it almost feels like a suspect centered approach to the findings. Raf's DNA is important, but not the presence of "at least" one other male, nor is he concerned of how many other males there could be.
He's also blind to the fact that there is no other physical evidence of anyone but Guede in the room. Fair enough to say his analysis is limited to the DNA on the clasp, but he seems to be drawing a connection to a finding of Raf's DNA, and actual guilt - i.e., how Raf's DNA got there. He says that's a question, but also discounts the possibility of contamination by saying 'people walking in and out of a room wouldn't be likely to cause contamination. He seems to be an advocate for guilt, rather than, or in addition to, being an objective source of info.
2. In furtherance to the above, Balding seems oddly unconcerned about other sources of contamination (not worried about reviewing negative controls, while dismissing the need for a second run).
He also complains about the problem of splitting a sample in two because it may jeopardize getting any result at all, and defends the reliability of using a single run. It's as though he's working to obtain a usable result, even of diminished reliability, rather than a reliable result. He has a preference for getting a result, over reliability. That seems to me a prosecution oriented POV.
His willingness to overlook issues like storage of the clasp strikes me as obtuse. He's not worried about the defense having an opportunity to validate or disqualify the result. It's like he wants the quick and dirty win, over the well proven point.
I don't think Balding is intentionally dishonest. But I do get the sense he is a subtly prejudiced witness in this matter.
