It’s not just the David Bain case where people look at the same evidence and see different things. As technology advances, juries are increasingly expected to grapple with complex scientific evidence and diverging expert opinions before reaching their verdict. In some cases, even lawyers and judges grapple with complex scientific evidence presented in court. Mike White asks whether 12 untrained individuals are capable of dealing with this, or if there’s a better way.

In October last year, Mark Lundy appealed again ( unsuccessfully ) against his conviction for murdering his wife, Christine, and seven-year-old daughter, Amber. But what was equally on trial in the Court of Appeal over three days was the role and reliability of scientific evidence in New Zealand’s justice system.

At his first trial in 2002, Lundy had been found guilty of the murders largely due to two specks on his shirt which the prosecution claimed were Christine’s brain tissue. This conclusion had been reached after testing using immunohistochemistry (IHC), which had never been employed forensically before.

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After his conviction was quashed by the Privy Council, the Crown radically altered its case against Lundy, including the timing and scenario for the murders, jettisoning evidence and many witnesses it had insisted were reliable until that point.

But at Lundy’s retrial in 2015, it retained the controversial IHC evidence and added another innovative scientific test on the two specks, involving what’s known as mRNA (messenger RNA). The test, performed in Holland, was so innovative it was created specifically for Lundy’s retrial. Not only had it never been done before, it had never even been peer-reviewed to ascertain its validity or dependability.

The evidence, which suggested the specks on Lundy’s shirt were more likely to have come from a human than other animal, were the subject of considerable controversy before and during Lundy’s retrial as to whether such novel and untested science should be heard by the jury.

But what made the mRNA evidence even more fraught was its extreme complexity, with experts for the Crown and defence arguing in rarefied language that even the lawyers and judge struggled to understand.