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Saturday, 21 February 2009

Canada: Scientific evidence challenged by Aziga's defence

Two months after the Crown rested its case against Johnson Aziga - accused of first-degree murder due to the death of two women with whom it is alleged he recklessly infected with HIV - his defence team is rigourously questioning the scientific evidence that the Crown had said linked Mr Aziga with the seven complainants allegedly infected with HIV (an additional four complainants allege that Mr Aziga had unprotected sex without disclosing his HIV status, but they are HIV-negative).

Previously, Paul Sandstrom, Director of National HIV and Retroviral Laboratories at the Public Health Agency of Canada, had testified that Mr Aziga and the seven HIV-positive complainants shared the same HIV subtype, clade A, which is rare in Canada but endemic in Uganda, where Mr Aziga is from.

Sandstrom's evidence was that Aziga and the women had viruses so genetically similar they would have come from a common ancestor. He said they formed a unique transmission cluster when compared to other clade A viruses in Canada and internationally.

(Source: The Canadian Press)

However, defence lawyer, Davies Bagambiire who is aware of the precedent-setting English case from 2006 which established that scientific evidence – specifically phylogenetic analysis – is not as cut and dried as other forensic tests relied upon by the criminal justice system, such as genetic fingerprinting.

The lawyer claimed police and prosecutors had “tunnel vision from the beginning to the end” of the case.

“The fact that there were other possible sources of the HIV for the women who tested positive was never even contemplated,” he said.

Bagambiire noted most of the women had met Aziga in “risky environments,” such as lower-class bars and night clubs in Hamilton and Brantford.

“The evidence is that other men could have been possible sources of the HIV,” said Bagambiire.

He pointed specifically to a Brantford man, who is the current partner of one of the HIV-positive women, and who subsequently was found to have had unprotected sex with both her and another complainant in this case.

“Some men who engaged in sexual activities with the complainants left the country without ever having been directed to take an HIV test. Some of their names are not known and their HIV status is not known,” he said.

Source: The Hamilton Spectator


MancSense said...

Johnson Aziga and questions about the virological evidence

Call a virologist

The defence lawyers failed to follow a key lesson from some recent English cases - which is to call a virologist, expert in HIV, as an expert witness, or at the very least commission an expert HIV virologist's report to use as evidence.

Because the state called Dr Paul Sandstrom, director of the Public Health Agency of Canada's national HIV and retrovirology laboratories as its scientific witness, there was a critical need to have an internationally respected independent expert HIV virologist giving evidence for the defence.

In well represented recent English cases, some level of expert HIV virologist involvement has led to a not guilty verdict, acquittal, case dismissed, and cases being abandoned. It makes a crucial difference to the outcome. It may not always cast enough reasonable doubt on all prosecution claims, but the English experience so far is all of prosecution failures where this is used, and usually of prosecution successes when it isn't used.

From my reading of reports about the scientific evidence an expert virologist would have been able to question, or even demolish the assumptions and conclusions put forward by the prosecution.
Here's the report of the testimony of Dr Sandstrom:

"We were able to determine that all of the complainants and Aziga had a phylogenetically distinct form of HIV and that Mr. Aziga had the virus prior to contact with any of the women," Sandstrom said. .....

Aziga and the women in the Hamilton infection cluster all had Clade A, which is rare in North America but endemic in Aziga's native Uganda.

In this country, fewer than 2 per cent of those newly diagnosed with HIV have subtype A.

Phylogenetic analysis examines small differences in HIV genes by coding sequences of the HIV genome and comparing them to other HIV sequences in public databases.

HIV virologists can only determine the degree of similarity between two samples. They can't produce a definitive match because unlike human DNA, HIV is not unique to an individual.

The analysis is also unable to determine the direction of transmission, Sandstrom said. So, theoretically, one of the women could have infected Aziga, instead of the other way around.

To resolve that issue, Sandstrom obtained a frozen blood-plasma sample drawn from Aziga after his HIV diagnosis 12 years ago. The specimen -- collected before Aziga met any of the women -- was phylogenetically analyzed and found to be nearly identical to the Hamilton infection cluster, comprising Aziga and the seven HIV-positive women.

"It means Mr. Aziga did not become infected by any of the women and that he had already been infected prior to contact with any of the women," Sandstrom said.

No Proof

This does not fully address or prove transmission from Johnson Aziga at all - other explanations are at least a possibility, and need to be ruled out. Mr Aziga and the women complainants are not the only people in Canada with subtype A - there are over 1000 other people diagnosed with it and more who are undiagnosed. One or more of the others with HIV-A might have been the source of one or more women's HIV.

Sandstrom did not consider it part of his job to explore this, or try to exclude this as a possibility. As the leading state HIV virologist he had a professional obligation to attempt to resolve this uncertainty and present the full picture. It would either have strengthened or weakened the prosecution case. Either way it needed checking.

Not my job to check

He was cross examined about this by the defence who argued that although Aziga and the women share a related virus, that did not mean that other persons, still unknown, might not also be carriers and part of the same transmission network. "It still remains, that your investigation does not rule out the possibility that there are other people 'out there' who are a part of the same infection cluster," suggested the lawyer. Sandstrom said his investigation was "not directed at finding additional complainants or additional suspects," but at providing confirmatory evidence for the footwork done by Hamilton police.

And the police, under cross examination, said it wasn't their job either, to look for other possible sources of the women's HIV.

Miscarriage of Justice and reversed burden of proof

This leaves me with serious concerns that there has been a miscarriage of justice. The defence is left to carry out an investigation, without police powers or resources, requiring the taking and testing of blood samples and complex and expensive scientific analysis, in an attempt to show there are other credible explanations. Does this not unfairly reverse the legal burden of proof?

Sexual history of complainants must be a central part of all transmission investigations

With HIV transmission cases, the proper police investigative practice of not looking into a rape complainant's own sexual history, is often adopted. A woman's sexual history is irrelevant to whether she was forced to have sex by someone; however it is critical to establishing which of her partners might have been the source of HIV in a consensual encounter. To attempt to prove X did it, you have to at least rule out A, B, C etc. And this at least can be proved conclusively with virology (HIV virology can prove someone didn't transmit that HIV, but it can't prove who did).

Rarely are the circumstances such that a complainat can be absolutely sure which of several partners might have been the source. The police are used to checking statements and seeking corroboration for everything. Why are claims about who transmitted HIV treated as if they cannot and must not be questionned? Why don't the police routinely seek, and prosecutors demand, corroboration by ruling out all other possibilities?

For example, one of the women who died (H.C.) had three previous partners in recent years, two of whom were also migrants from Africa and, if HIV positive, likely also to have HIV-A. And an earlier date of infection from one of these men would better explain her surprisingly rapid development and death from Burkitt's lymphoma, all apparently within 3 years or so of her supposed infection by him. ( and from reports in The Hamilton Spectator and then search for Aziga, HIV)
And regarding the other women, see for example

Reasonable doubt opportunity wasted

With prosecution and defence expert witnesses contradicting each other, reasonable doubt would be raised far more strongly. Instead of calling an expert in HIV virology, the defence called Rafal Kustra, an associate professor of biostatistics with the Dalla Lana School of Public Health at the University of Toronto. He was not able to make much of an impact, saying he was "underwhelmed" by the level of analysis used by Ottawa scientists who concluded that Johnson Aziga and seven HIV- positive women carry viruses that are so closely related they can be described as a single "Hamilton transmission cluster." He criticised the method used by Sandstrom and that was about it. He didn't produce any new evidence, and wasn't even invited by the defence to offer a different interpretation of the same facts, or say what further evidence was needed, and which questions need to be answered, before the prosecution's case can become credible scientifically.

The defence barrister did criticise the prosecution's scientific claims and failure to eliminate other potential sources of HIV. This does not carry any real weight with judge and jury - in legal terms it is not evidence, more an argument. The defence lawyer is not a scientific expert who can credibly contradict Canada's head of HIV virology, no matter how right he may be. He tried, but didn't call an expert virologist as a witness who could have made the argument convincing with fresh evidence and interpretation based on professional expertise.

An independent expert virologist might have been able to show, for one or more of the infected, scientific reasons why the prosecution are drawing the wrong conclusions and missing out vital evidence.

Establishing reasonable doubt is the job of the defence. Succeed, and the judge would then have pointed this out to the jury. The judge's response to reasonable doubts should lead to a not guilty verdict, or acquittal, on one or more of the charges.

Not guilty verdicts and acquittals might not have produced justice, but there doesn't seem to be much certainty of justice in this verdict, from what I have seen reported.

No-one knows for a scientific fact whether or not he did transmit HIV to the 7 people whom the prosecution claim he infected. This can never be proved with current scientific techniques. The essential virological analyses and testing of other partners, that might have shown the virological connections between the HIV samples could have more than one credible explanation, seem to have been omitted.

The apparent failure to eliminate from suspicion the women's other / previous partners raises serious doubts about any scientific claims made that he was the source, because those claims seem based on only some of the potential scientific evidence.

Herd mentality
A herd mentality can develop in big trials and high profile cases. The pressures to secure a conviction are huge. In cases involving HIV transmission, some of the media behave like a baying mob. Police and prosecutors may become convinced they have their man and be unable to entertain any other possibility. We've much experience of this in England - – and this case has the hallmarks of another, but in Canada.

Dysfunctional justice?

It's a case that shines a light on the Canadian justice performing badly in a major trial. It seems there are errors as much in the prosecution, police investigation and justice procedures, as well as tactical mistakes by the defence. He's been five years in prison awaiting trial and this was his 6th team of lawyers. This case makes the Canadian justice system look dysfunctional. I hope it redeems itself at the appeal stage.

See also


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