The language of forensic science

A forensic scientist examines the language that gives technical experts such strong authority in court

The jury in the Philip Polkinghorne murder trial has heard from drug analysts, DNA scientists, and even a mechanical engineer about power spikes from using a toaster.

Is there anything science can't reveal when it comes to such tricky court cases?

Well, yes.

Forensics is a tool, but not the instant-answer, 'gotcha' link showcased on TV procedurals and in crime novels.

"I think forensic science has actually gone through a little bit of a crisis, internationally," says Paige McElhinney, Director of The Forensics Group Ltd.

"We've actually looked at ourselves and said, 'do we have data to actually support what we're saying? Do we have the right information to be able to say something is likely or unlikely?' These are key kind of phrases where people hear them and think 'gosh a scientist is saying something's likely, there must be some sort of data or something to support that'. So we're really looking at what we're actually saying, the words that we're using, how we're presenting findings, to make sure that we are expressing uncertainty where we should be."

Today on The Detail, McElhinney, who's been working as a forensic scientist for more than 20 years, explains why her field isn't as black and white as many assume.

In the Polkinghorne case, jurors are now being asked to untangle evidence they've heard over the past two months.

The key questions is, how did his wife die? The Crown alleges Polkinghorne murdered Pauline Hanna; the defence says she died by suicide.

So why, when we have science that can detect DNA in a speck of blood, can't we know the cause of death with absolute certainty?

"It's a hard one because you would think something like cause of death would be a clear-cut answer, but sometimes science doesn't have an answer," says McElhinney.

"I think we've all grown up as a generation on true crime, on crime dramas, on forensic science... a really easy answer for every single investigation - science solving crimes."

But, she says: "science doesn't solve crimes. It's a tool to assist in the investigation of crimes."

She can't speak to the Polkinghorne trial specifically, but gives context around the limits of her field, including how juries can be expected to sort through opposing opinions about one piece of evidence.

"The fact that there's two opposing opinions makes it more difficult because it's now left to a jury to decide which of those experts they believe more, which of those experts they like more, and you're asking lay people to make a decision on cause of death with really no experience or training."

Despite this, she says it's her job to make the science clear and to add context.

"I think it's really important that any expert is a science communicator. It's not dumbing down, you have to make yourself understandable. It helps nobody to make your findings complicated.

"It's also putting that science in that context. So while you may have a DNA analyst get on the stand and give evidence that DNA was detected, the jury need to consider that that might not answer any questions.

"We can't answer how it was transferred or when it was transferred, and it's up to the jury to know that there are limitations to those scientific findings."

McElhinney consults for defence counsel, though in the past she's worked for the prosecution. She says assisting defence counsel is something she and her colleagues are often criticised for.

"At the end of the day if we prevent even only one miscarriage of justice or we make sure the right person gets convicted - then it's all worth it," she says.

Like all science, forensics is constantly evolving. But while some changes in recent years have been an advancement, others have been more of a reckoning.

In this episode, McElhinney gives examples of some of the more fallible areas of her field, including bite mark analysis; and tells us why fingerprint identification isn't necessarily identification.

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