How farm-based fieldwork could pave the way for more accurate forensic timelines

A forensic scientist’s fieldwork on a family farm may help reshape how investigators determine time of death of humans — one of the most critical and contested elements in criminal cases.

Dr Donna McIntyre, who recently completed her PhD at Federation, spent several years exploring what happens to a body after death, investigating how insects, microbes and odours interact as decomposition unfolds and how those interactions affect estimates of the postmortem interval (PMI) – the term to describe the time since death.

Accurate PMI estimates are vital in criminal investigations, helping to establish a time frame for forensic examiners to analyse evidence such as CCTV footage and mobile phone records and can confirm or challenge alibis.

Dr McIntyre’s study began with a literature review where she read “hundreds and hundreds” of forensic science papers spanning entomology, microbial activity and volatile organic compounds (VOCs) — the odours released as a body breaks down.

There has been extensive research on each of these fields individually and some studies explored the combined effect of insects and VOCs but none the effects of insects, microbes and odours together.

“That’s what became my research question,” Dr McIntyre said. “How do these really important drivers of variation impact the postmortem interval when you look at them as a whole?”

The study called for a decomposition trial under controlled conditions. Human bodies for research are tightly regulated leading Dr McIntyre to the next best thing for this job: pigs. The animals’ physiology, especially their skin composition and size ratio, make them the closest non-human analogue for forensic work.

Pigs that had died from natural causes were ethically sourced from a farm and Dr McIntyre was able to set up an outdoor laboratory at a farm owned by her family.

Dr McIntyre set up four treatment groups to test how different factors influence the breakdown of a body by comparing four conditions. A natural control left to decompose on its own, an insect‑exclusion setup using fine mesh to keep bugs out, a microbe‑reduction treatment where the body was washed with chlorhexidine but still exposed to insects, and a ‘double‑exclusion’ scenario that combined the antimicrobial wash with insect‑blocking mesh to limit both microbial action and insect activity.

Decomposition was monitored daily, measuring mass loss — using racks and suspended ropes to weigh the carcasses — and a ‘total body score’ — a system that assigns visual ratings to different stages of decay.

At specific timepoints, Dr McIntyre also analysed microbial activity, insect presence and VOC profiles, aiming to build a comprehensive picture of how decomposition progressed across the four treatment groups. 

Insects accelerate decomposition by colonising the body, laying eggs and consuming soft tissue. Microbes and VOCs also play major roles by isolating and combining these factors. Dr McIntyre hoped to see how each influenced the others over time.

The results revealed strong interactions between microbes, insects and odours as decomposition progresses. Together, the findings challenge the reliability of simple decay models and instead support a more multifactorial approach — one that accounts for biological interactions and environmental context when estimating time since death.

The changes to microbial communities and the exclusion of insects significantly altered both the composition of microbes and the odours released during decomposition, which in turn affected how insects colonised the remains. Preventing insect access notably slowed decomposition — based on total body score and mass loss — while altering microbial communities disrupted normal odour patterns.

The study highlights the importance of microbial–insect dynamics and points to the ‘necrobiome’ framework as a powerful way to understand decomposition. These insights could help improve the accuracy of forensic investigations.

The publication will allow other researchers to replicate and expand on the findings, helping to establish a stronger evidence base. Over time, this could support the integration of these approaches into forensic investigations.

Dr McIntyre said a more holistic understanding of decomposition could strengthen courtroom evidence, reduce uncertainty in investigations and provide more accurate timelines for families seeking answers.

“Having an accurate PMI can help confirm or negate alibis,” McIntyre said. “It gives you really good insight not only into time of death, but potentially where the death might have happened.”

Career inspiration in an unexpected place

Dr McIntyre’s interest in forensics began in an unexpected time and place.

“I remember watching Dexter as a kid on TV and that’s what first got me interested in forensics.”

Later, other students would be “moaning and groaning” through three-hour forensic psychology lectures – her favourite class.

“I love forensics. I love learning all about the different types of forensics, forensic psychology and how to present forensics in court.”

Dr McIntyre also worked at the Ballarat Regional Integrated Cancer Centre through an internship with the Victorian Comprehensive Cancer Centre (VCCC) Alliance where she was involved in clinical trials. It was her colleagues there who inspired her to pursue her PhD.

Dr McIntyre now works in clinical trials at Thermo Fisher Scientific, travelling across Australia to ensure hospitals and research sites follow strict protocols. Her PhD, she says, has made her a stronger critical thinker and given her a deeper understanding of research design.

“It’s essentially the job of an auditor, making sure that the sites are compliant with the essential documents and protocols in the trial, and compliant with regulations in Australia as well as global regulations,” she said.

Forensics remains her passion and is a subject she is keen to return to.

“The research that I've done, it does go beyond PMI. Being able to show interactions between these drivers of variation in decay, there's a plethora of area other areas that I could delve more into with more research.”