Surreal illustration of collagen degradation in a forensic context

Unlocking the Past: Can Collagen Degradation Solve Forensic Mysteries?

Lena Voss in Law & Justice August 2025 • 4 min read.

"A new survey explores how analyzing collagen in bones could provide crucial clues for determining time of death in forensic investigations."

In forensic science, accurately estimating the post-mortem interval (PMI)—the time elapsed since death—of unidentified human skeletal remains is a significant challenge. Current methods often fall short, leaving investigators with broad estimations. This is where the study of collagen degradation comes into play, offering a potentially more precise tool for unlocking the secrets held within bones.

Collagen, the main structural protein in bones, degrades over time due to environmental factors and microbial activity. Scientists are exploring whether the rate of collagen degradation can be predictably linked to the PMI. If so, analyzing the state of collagen in skeletal remains could provide a reliable 'clock' to determine how long ago death occurred.

Building on prior research using animal bones, a recent survey has shifted focus to human bones. This survey aims to reproduce and refine methods for measuring collagen degradation, specifically focusing on the ratio of collagen to non-collagen (Co/NCo) in bone samples. The ultimate goal is to develop a practical and accurate technique for forensic experts.

Decoding Bone Clocks: How Does Collagen Degradation Work?

Surreal illustration of collagen degradation in a forensic context

The study, published in Legal Medicine, details an attempt to adapt a method initially tested on porcine bones to human remains. The researchers analyzed 37 human bone samples from forensic contexts and 11 archaeological samples with known PMIs. They prepared thin bone sections, stained them to differentiate collagen from other proteins, and then used spectrophotometry and stereomicroscopy with digital imaging to analyze the Co/NCo ratio.

Spectrophotometry, which measures light absorption, yielded Co/NCo ratios much lower than expected. This led the researchers to focus on stereomicroscopy and digital imaging, a method they had previously refined on porcine bones. This technique involves visually analyzing the stained bone sections under a microscope and using digital software to quantify the ratio of red (collagen) to green (non-collagen) areas.

Sample Collection: Femoral bones from 35 deceased individuals exhumed from graveyards (PMI ranged from 21-48 years) and 2 fresh samples were collected during autopsies.
Bone Preparation: Ring-shaped bone pieces were sawed out, stabilized in resin, hardened, and thin sections of 250 µm were prepared using a microtome.
Staining and Analysis: Bone sections were stained with Sirius Red/Fast Green to differentiate collagen (red) from non-collagenous proteins (green).
Photometric Analysis (Initial Attempt): An initial attempt to measure the Co/NCo ratio using spectrophotometry yielded results that were inconsistent with expected values and previous porcine bone studies.
Stereomicroscopic Analysis: A new method involving stereomicroscopy and digital imaging was used to quantify the red/green ratio, providing a semi-quantitative assessment of collagen degradation.

While the study did find a significant reduction in the Co/NCo ratio correlating to PMI in male individuals, the findings were not conclusive enough for immediate forensic application. The authors emphasize the need for more extensive reference data and practical experience before this method can be reliably used in forensic casework.

The Road Ahead: Refining the Bone Clock

This survey underscores both the potential and the challenges of using collagen degradation as a forensic tool. While the stereomicroscopy method showed promising results, further research is crucial. Future studies should focus on expanding reference datasets, accounting for factors like sex, age, and environmental conditions, and refining the analytical techniques. Only then can we unlock the full potential of the 'bone clock' and provide more accurate PMI estimations in forensic investigations.

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This article is based on research published under:

DOI-LINK: 10.1016/j.legalmed.2018.11.009, Alternate LINK

Title: Collagen Degradation As A Possibility To Determine The Post-Mortem Interval (Pmi) Of Human Bones In A Forensic Context – A Survey

Subject: Issues, ethics and legal aspects

Journal: Legal Medicine

Publisher: Elsevier BV

Authors: Katharina Jellinghaus, Petra Kathrin Urban, Carolin Hachmann, Michael Bohnert, Gerhard Hotz, Wilfried Rosendahl, Ursula Wittwer-Backofen

Published: 2019-02-01

Everything You Need To Know

Why is accurately determining the post-mortem interval (PMI) so difficult in forensic investigations involving skeletal remains?

Estimating the post-mortem interval (PMI) from skeletal remains is challenging because current methods often provide broad estimations. Environmental factors and microbial activity affect the decomposition process in complex ways. The study of collagen degradation offers a potential avenue for more precise PMI estimation by analyzing the state of collagen in bone samples.

How does collagen degradation in bones potentially serve as a 'bone clock' for forensic scientists?

Collagen, the primary structural protein in bones, degrades over time. Scientists are exploring whether the rate of collagen degradation can be predictably linked to the post-mortem interval (PMI). By analyzing the ratio of collagen to non-collagen (Co/NCo) in bone samples, forensic scientists aim to establish a reliable 'clock' to determine how long ago death occurred. The stereomicroscopy method involves visually analyzing stained bone sections under a microscope and using digital software to quantify the ratio of red (collagen) to green (non-collagen) areas. Spectrophotometry is another method that measures light absorption to yield Co/NCo ratios.

What methods were used to analyze collagen degradation in human bone samples, and what challenges did the researchers encounter?

Researchers used spectrophotometry and stereomicroscopy with digital imaging to analyze the collagen to non-collagen (Co/NCo) ratio in human bone samples. Spectrophotometry yielded Co/NCo ratios much lower than expected, leading the researchers to focus on stereomicroscopy and digital imaging. This technique involves visually analyzing the stained bone sections under a microscope and using digital software to quantify the ratio of red (collagen) to green (non-collagen) areas. Challenges included the need for more extensive reference data and the influence of factors like sex, age, and environmental conditions.

What are the implications of using collagen degradation analysis to estimate the post-mortem interval (PMI) in forensic science?

Using collagen degradation analysis to estimate the post-mortem interval (PMI) could significantly improve the accuracy of forensic investigations involving unidentified human skeletal remains. By establishing a more reliable 'bone clock' based on the ratio of collagen to non-collagen (Co/NCo), forensic experts may be able to provide more precise PMI estimations. This could aid in identifying victims, reconstructing events, and ultimately, advancing the pursuit of justice. However, the method requires further refinement and the development of extensive reference datasets to account for various factors such as sex, age, and environmental conditions.

What steps are necessary before collagen degradation analysis can be reliably used in forensic casework?

Before collagen degradation analysis can be reliably used in forensic casework, several steps are necessary. The method involving stereomicroscopy requires further research to expand reference datasets. Researchers need to account for factors like sex, age, and environmental conditions that may influence the degradation rate of collagen. Analytical techniques also need refinement to improve accuracy and consistency. Once these steps are taken, the 'bone clock' can reach its full potential in providing more accurate post-mortem interval (PMI) estimations.