I disagree in several respects.I get the point about transfer being possible, but the problem here is the expert was clear there were no signs of a mixed sample.
Saying the DNA ‘might have come from several men’ doesn’t line up with the actual profile of 26/27 and then 27/27 markers matching Singh as a very strong hit.
Y‑DNA can technically come from different men, but only if they’re in the same paternal line or if there’s a clear mixture in the sample (which there wasn’t). The stick/dog scenario is speculative without evidence that Singh handled it. And under cross‑examination, the expert confirmed it couldn’t have come from Marco.
Stronger DNA under nails usually comes from direct physical contact and object transfer tends to leave weaker, mixed traces. We have to weigh our thoughts up against the strength of the lab tested match and the expert testimony.
Yes, the NZ expert Patel said that she found no signs of the DNA (from the fingernail) being mixed. That's not the same as saying that the DNA showed signs of being unmixed. I don't mean that her observation about the lack of signal is of no relevance or value, but there's no information about how probable/improbable it would be that a sample of mixed DNA should show no technical signal of being mixed. In fact I doubt that she'd be repeatedly qualifying her answer with "if you assume they're from one individual", "if you assume those results originated from one male" if the sample provided its own proof that the Y-chromosome material came from only one person.
I feel like we're not on the same page about the Y-DNA and different men. What I think Patel means, is that if the sample is from one man, and there are say 26 matches, that's 26 out of 27 which is a high score. But if the sample comes from 2 men, then perhaps--I'm making up these numbers--that's 20 out of 27 from one, 12 out of 27 from another, with an overlap of 6 from both. So Singh's Y-DNA would not be a particularly good match for that of either of the two contributors, yet it would appear to match the sample. I don't know if it could work like that, I'm just trying to understand why the expert says what she does.
I do think there is DNA evidence that both Singh and Toyah handled the stick.
Forensic scientist Angelina Keller told the court it was 3.7 billion times more likely than not that Mr Singh had contributed DNA to a two-person mixture found on a stick at Ms Cordingley's burial site.
"Up to approximately 1 in 3.7 billion people could give the same [likelihood ratio] as that, or greater," Ms Keller said.
Ms Cordingley was more than 100 billion times more likely than not to have been the other contributor to that mixture.
DNA samples found near Toyah Cordingley burial site scrutinised
The former nurse accused of the 2018 murder of Toyah Cordingley was 3.7 billion times more likely than not to have contributed to a DNA sample found on a stick where she was buried, his trial has heard.
I just want to say again Patel's evidence was not that the fingernail DNA came from under the nails. She said she didn't know where it had been located on the nail. I don't know where the "under the nail" allegation is coming from. Perhaps there's another expert who collected the biological material who gave evidence about that.Stronger DNA under nails usually comes from direct physical contact and object transfer tends to leave weaker, mixed traces. We have to weigh our thoughts up against the strength of the lab tested match and the expert testimony.