What happens to a dead body in an extremely cold environment? Does it decompose? How do these conditions affect how forensic scientists understand when the person died?
Estimating the time of death, also known as the post-mortem interval, is a complex task. It plays an important role in forensic investigations because it can provide critical insights into the timeline of events leading up to a person’s death. This information can narrow down potential scenarios and suspects, helping to solve criminal cases.
Many factors play a role in death, ranging from environmental conditions to the individual’s premortem health. Historically, scientists estimated the time of death by observing postmortem physical and biological changes in the body, such as stiffening, fluid retention, and cooling.
However, these methods are limited by their variability and dependence on external factors. Calculating the post-mortem interval became more accurate with the advent of molecular biology. But it is still a challenging task, especially in extremely cold weather conditions. There are often no clear signs of decomposition on a frozen body during the first months after death.
We are forensic scientists who lead the forensic programs at the University of North Dakota and the University of Central Lancashire. We use molecular biology and bioinformatics to develop tools that allow investigators and detectives to more accurately estimate the post-mortem interval. Our recently published research in Frontiers in Microbiology showed that studying the microbes involved in decomposition can predict the time since death in extremely cold conditions with high accuracy.
Decomposition in cold environments
Our research took place in Grand Forks, North Dakota, one of the coldest cities in the United States, where winters are characterized by temperatures that can drop to -40 degrees Fahrenheit (-40 degrees Celsius) and strong winds that can reach 30 miles per hour (50 kilometers per hour).
In an extremely cold environment like North Dakota winters, traditional methods may not be sufficient to understand decomposition and estimate time of death. For example, the body cools much faster in cold conditions, which can skew estimates based on body temperature.
Likewise, cold environments can delay the onset and duration of rigor mortis, or body stiffness. The decomposition process, including the activity of insects and other scavengers that contribute to the breakdown of the body, can also be slowed or stopped by freezing temperatures.
Snow is another important factor in studying decomposition. It can insulate a body by trapping residual heat and raising its temperature slightly above its surroundings. This insulating effect causes the body to decompose more slowly than bodies exposed to the open air.
Microbes and time since death
In extreme cold, it is necessary to use additional tools to understand decomposition and estimate the time of death. Advanced molecular techniques, such as analyzing the microbiome, gene expression and protein degradation, can provide valuable information about the crime scene.
Every organism has specific microbial characteristics that act as a fingerprint. The necrobiome, a community of microbes associated with decomposing remains, plays a crucial role in decay. Specific microbes are present during different stages of decomposition, helping to break down tissues and recycle nutrients. Forensic scientists can sample which microbes are living in a dead body to infer how long ago someone died based on the composition of the microbial population.
Our study aimed to identify common patterns in the microbial changes that occur during decomposition in extremely cold environments. Over a period of 23 weeks, we collected and analyzed 393 samples of microbes from inside and outside the noses of dead pigs covered in snow. Pigs decompose in a similar way to humans and are widely used in forensic investigations. We developed models to estimate the post-mortem interval by linking microbial genetic data to environmental data such as snow depth and outside temperature.
Overall, we found that the bacterial species Psychrobacter, Pseudomonas And Cancer bacteria can best predict the time after death under extreme winter conditions, up to six months after death, with a margin of error of just over nine days.
We found that different bacterial species were most abundant at different time intervals. For example, levels of Psychrobacter They increase five weeks after death and are most numerous after ten weeks, while Pseudomonas increases between weeks five and nine and peaks around week eighteen.
Improving forensic investigation
Death is often an uncomfortable topic to bring up in conversation. But from a forensic perspective, techniques and methods to determine when someone has died can help bring justice and peace to loved ones.
Our research showed that even in cold environments, decomposition does not stop completely. By studying the microenvironment – the local conditions surrounding the body, including temperature, humidity, and microbial activity – we can reveal crucial information about the decomposition process. The key microbial species we identified served as biomarkers of death, allowing us to develop models of time of death that researchers can use to overcome the limitations of visually examining remains alone.
Microbes can become a crucial piece of the puzzle during a death investigation, helping to establish more accurate timelines, even in extreme circumstances.
This article is republished from The Conversation, a nonprofit, independent news organization that brings you facts and reliable analysis to help you understand our complex world. It was written by: Noemi Procopio, University of Central Lancashire and Lavinia Iancu, University of North Dakota
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Noemi Procopio does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond her academic appointment. She receives funding from UKRI (Future Leaders Fellowship MR/S032878/1).
Lavinia Iancu does not work for, consult for, own stock in, or receive funding from any company or organization that would benefit from this article. Furthermore, she has disclosed no relevant affiliations beyond her academic appointment.