What did we learn from ESR forensic scientist Nicholas Curnow, the Crown's DNA expert?

• Pauline Hanna's neck had DNA from both herself, Polkinghorne, and a much smaller amount, possibly from a third person.
• DNA testing is extremely sensitive and DNA can be transferred indirectly, via intermediary objects.
• There were no conclusive results from the analysis of seven samples from the two orange ropes found at the scene.

The trial will resume at 10am tomorrow. The jury was not told who the Crown will call as its first witness tomorrow.

Justice Lang has concluded proceedings for today.

The trial will resume at 10am tomorrow. The jury was not told who the Crown will call next, when proceedings resume on Tuesday.

Mansfield is asking why the protocols changed. ESR forensic scientist Nicholas Curnow said it was found other substances could cause false positives, so they made their guidelines more conservative.

DNA testing is very sensitive, Curnow said. But they had shown through experience and validation that the male specific test is slightly more sensitive, the scientist said.

That meant they could get results from smaller amounts compared to the standard tests.

"Is it fair to say that the male specific DNA analysis is extremely sensitive?" defence lawyer Ron Mansfield asked.

"Yes, it's very sensitive."

"If we touch a surface or we touch another person, we might leave behind our DNA?" asked Mansfield.

"That's correct." Curnow said.

Curnow confirmed they were unable to age the DNA.

"It could have been there for minutes, hours or days, or even much longer than that?"

"That's correct."

"You can't tell us how the DNA"s go there either?"

"No, that's one of the limitations," Curnow said.

"Is there potential for DNA for one individual to get on another object or a person without there being a formal touch?"

"Yes, what you're referring to their is indirect transfer."

Curnow is using a cup to illustrate his point. He could touch a cup, hand it to Mansfield, and transfer his DNA to Mansfield.

That ends Curnow's cross-examination, there's nothing further from the Crown Solicitor, and that ends his evidence.

Now, finally, Crown prosecutor Alysha McClintock is on to the frequently mentioned brown stain on the fitted sheet on Hanna's mattress, which tested positive for probable blood.

"A low-level and partial DNA profile was obtained which corresponded to Mr Polkinghorne’s reference DNA profile," ESR forensic scientist Nicholas Curnow said. 

McClintock has finished her questioning of Curnow so we move on to Mansfield's cross-examination.

[from earlier in the blog: Each of those samples from her neck did give a weak positive result from a chemical test for blood. That was then reported as possibly a blood stain. ESR has since updated reporting guidelines, meaning Curnow would now report the samples as "inconclusive" for blood as a result of its new protocols.]

Samples from Pauline Hanna's neck were tested with both standard DNA analysis and the male-specific Y STR analysis.

The sample from the left of her neck had results from three people. They were Hanna herself, and Polkinghorne, plus a much smaller amount that could have originated from a third person.

The Y STR analysis showed the DNA could have come from Polkinghorne, ESR forensic scientist Nicholas Curnow said.

There was no indication that there was any more than one male's DNA present, Curnow said.

Turning to the sample on the left-hand side of the neck, low-level DNA from at least two people was found, explained by a mixing of DNA from Hanna and Polkinghorne.

The right neck sample's Y STR analysis showed the male DNA could have come from Polkinghorne.

Blood stains from fingernail clippings were low-level and partial and could have originated from Hanna.

Now the focus moves on to the DNA testing of the ropes, and an answer to the question raised in Matheson's cross-examination.

Curnow said there were seven samples taken from the two sections of orange rope.

"Were there any results that were able to be linked to anyone?" asked Crown solicitor Alysha McClintock.

"In short, no," Curnow replied.

Both types of DNA testing were conducted. Standard analysis returned no profiling results.

Male-specific DNA testing showed either no results or results that weren’t suitable for comparison purposes, Curnow said.

There were indications in some DNA results that there could have been more than one male present, but they were ultimately inconclusive and not suitable for comparison purposes, Curnow said.

ESR forensic scientist Nicholas Curnow used two types of DNA testing.

They were the standard profiling DNA analysis used in most cases, and Y STR DNA profiling, used to analyse DNA from the Y chromosome found only in males, Curnow said.

The second type of testing for just male DNA is useful if you only want to look at the male DNA sample in a sample rich in female DNA, Curnow said.

He was asked to test samples from the left, index and middle fingers, along with samples from either side of her neck.

Each of those samples from her neck did give a weak positive result from a chemical test for blood. That was then reported as possibly a blood stain. ESR has since updated reporting guidelines, meaning Curnow would now report the samples as "inconclusive" for blood, as a result of its new protocols.

Samples from Hanna's left index and middle fingers did have the visual appearance of blood and gave a positive result for blood.

The Crown has now called ESR forensic scientist Nicholas Curnow. 

He is the forensic scientist who ESR forensic scientist Fiona Matheson earlier said would be better placed to answer questions relating to DNA.

Auckland Crown solicitor Alysha McClintock is leading the evidence-in-chief of Curnow, who joined ESR in 2009, and specialises in DNA analysis.

He is one of two forensic scientists who have analysed DNA samples taken by Matheson.

Philip Polkinghorne told detectives he found his wife on a chair in the entranceway, having hanged herself leaning forward while sitting in the chair with her neck tied in a belt, itself tied to an orange rope.

That means the hanging would amount to a partial suspension, like a prison hanging, rather than a full suspension hanging as used in executions.

Defence lawyer Ron Mansfield repeatedly suggested in cross-examination that the urine stains on the dressing gown, focused around the lower back of the gown, support the scenario of her dying in the chair as she hanged herself.

ESR forensic scientist Fiona Matheson said the Polkinghorne home was one of the largest scenes she had ever examined in terms of a residential home.

It is not possible to age when blood staining is deposited, Matheson said.

There were no further questions for Matheson, who has been discharged after nearly two days in the witness box across Friday and Monday.

Questions are now coming from Auckland Crown solicitor Alysha McClintock about the urine staining on the dressing gown that has become the key piece of evidence to emerge this afternoon.

"The scenario is that Ms Hanna was lying down. What, if anything, are you able to say about the urine staining – if indeed that's what it is?" McClintock asked.

"I'm very reluctant to form a comment about that, primarily because I'm not confident the staining is urine," Matheson said.

There were also a number of variables that led to more uncertainty about the path of the urine.

Now a bit of a curveball.

Defence lawyer Ron Mansfield has referenced an analysis, not yet mentioned at the trial in evidence, conducted in 2023 of a red mark on another set of stairs that ESR forensic scientist Fiona Matheson had tested and found not to contain blood. He said the analysis showed the red mark did contain blood – Polkinghorne's.

"Have you got any comment that you’d like to make on that?" Mansfield asked.

"I carried out an examination of the area described. I found no blood," Matheson said.

It is clear there is more discussion to come on this piece of evidence.

Mansfield has now finished his cross-examination.

Auckland Crown solicitor Alysha McClintock now has some questions in reply, relating to luminol testing.

The stain detected on the floor under Hanna's head was probably blood, detected with luminol, Matheson said.

Now there are questions from the Crown on urine or faeces testing from upstairs, and signs of blood downstairs.

There were no signs of bloodstaining aside from that under her head, Matheson said. There were no signs of urine or faeces staining upstairs either, the scientist said.