Hyperspectral Imaging In Forensic Investigations: Applications And Case Studies

By John Oncea, Editor

Hyperspectral imaging is a powerful tool for forensic investigations, offering a non-destructive, highly sensitive, and comprehensive approach to evidence analysis.

A while back, we took a look at how infrared technology was used to help take down the Maple Mafia. Today, we’re revisiting the field of forensics, this time digging into the role hyperspectral imaging (HSI) plays in helping solve crime.

For starters, did you know that forensic investigators use HSI to detect, identify, and analyze various substances and evidence, including bloodstains, bruises, paint, and documents? Or that HSI can analyze the spectral signatures of materials, providing detailed information that traditional imaging methods miss, even for materials invisible to the naked eye?

It also can help identify and analyze gunshot residue, aiding in the reconstruction of crime scenes and the identification of suspects, as well as detect and analyze latent fingerprints, even those that are faint or on challenging surfaces. 

Not only can HSI provide forensic investigators with the above-mentioned benefits, it does so in a non-destructive manner, allowing for the analysis of evidence without damaging it. It’s also highly sensitive, allowing it to detect even small or faint traces of evidence.

Biological Evidence Detection And Analysis

HSI represents a revolutionary advancement in forensic science, offering non-contact, non-destructive analysis capabilities that preserve evidence integrity while providing detailed spectral information across multiple wavelengths.

While this technology is still emerging in practical forensic applications, research studies and pilot implementations have demonstrated significant potential for solving various types of criminal investigations.

The technology’s ability to detect materials and substances invisible to conventional photography has opened new avenues for evidence analysis, from bloodstain pattern analysis to drug detection at crime scenes.

HSI has shown remarkable capabilities in bloodstain detection and analysis, addressing one of the most critical aspects of violent crime investigations. Research has demonstrated that HSI can quickly identify blood stains at crime scenes without the need for chemical treatments that might contaminate or alter the evidence, Specim writes.

The technology operates by detecting specific spectral signatures of heme components in the 500-700 nm range, allowing investigators to distinguish blood from other red substances that might appear similar under normal lighting conditions, the National Center for Biotechnology Information adds.

A comprehensive study involving 225 blood and non-blood samples demonstrated the technology’s effectiveness in differentiating actual blood from substances like ketchup, rust, red paint, nail polish, and fake blood across various substrates, including white cotton fabric, white tiles, and PVC wall sheets. The research utilized samples from multiple donors and tracked aging effects over three days, showing that HSI could maintain accuracy even as bloodstains aged and their visual characteristics changed.

The study employed advanced machine learning algorithms, including Support Vector Machines (SVM), Artificial Neural Networks (ANN), and Random Forest classifiers to achieve high accuracy rates in blood identification.

Furthermore, HSI has proven valuable in age estimation of bloodstains, a critical factor in crime scene reconstruction. The technology can help determine whether a bloodstain is from a recent incident or from an older event, such as distinguishing between blood from a current crime and blood from a previous nosebleed. This capability is particularly important in cases where multiple incidents may have occurred in the same location or when establishing timelines of criminal activity.

Fingerprint Detection And Enhancement

The development of specialized HSI systems has revolutionized fingerprint detection capabilities in forensic investigations. A notable advancement came through collaborative research between Waseda University, JFE Techno Research Corporation, and the National Research Institute of Police Science, which resulted in the creation of a “Forensic Hyperspectral Imager” device, ScienceDaily reports. This compact system, designed to fit in a suitcase for field deployment, can detect untreated latent fingerprints from challenging surfaces, including walls and magnetic strips of railway tickets.

The system’s ability to detect signals from fats and amino acids in fingerprints without physical contact represents a significant advancement over traditional fingerprint enhancement methods. Research studies have demonstrated the technology’s effectiveness in detecting blood-stained fingerprints using visible wavelength reflectance HSI, comparing favorably with chemical enhancement methods like Acid Black 1, adds ScienceDirect. The technology has shown particular promise in differentiating layered fingerprints into individual prints, which is crucial in cases where multiple individuals have touched the same surface.

Studies also have explored the detection of bloodstained fingerprints across various substrates, demonstrating the technology’s versatility in different crime scene environments. The non-contact nature of HSI preserves the original fingerprint patterns while providing detailed spectral information that can enhance identification accuracy and reliability.

Ballistics And Weapons Evidence

HSI has emerged as a powerful tool for gunshot residue (GSR) detection and analysis, addressing critical limitations of traditional chemical visualization methods. Conventional GSR analysis often involves applying chemicals that can alter or destroy the delicate residue patterns essential for reconstructing shooting scenarios, including determining shooting distances and angles. HSI provides a non-contact alternative that preserves these crucial patterns while enabling rapid detection and visualization of gunshot residue.

Research has demonstrated the application of HSI techniques for screening gunshot residue on skin using Attenuated Total Reflection Fourier Transform Infrared (ATR FT-IR) hyperspectral microscopy. This approach allows forensic investigators to examine potential GSR evidence without risk of contamination or alteration, preserving the evidence for subsequent analyses. The technology also has been applied in combination with machine learning methods for pattern detection, enabling more sophisticated analysis of residue distribution patterns that can provide insights into weapon type, firing distance, and shooter position.

Advanced studies have explored novel two-step methods combining fast fluorescence imaging with Raman microspectroscopic identification for detecting organic gunshot residue components. This multi-modal approach enhances the reliability and specificity of GSR detection, particularly important in cases where traditional methods might produce ambiguous results.

Drug And Chemical Substance Detection

HSI has proven effective in detecting trace amounts of explosive materials and drugs, applications particularly relevant to terrorism investigations and drug-related crimes. Research has demonstrated the detection of explosive residues on banknote surfaces using Raman HSI combined with independent component analysis. This capability is crucial for tracking the movement of explosive materials and identifying individuals who have handled such substances.

The SHERLOC (Hyperspectral Laser Imager for Scientific Investigation and Detection of Evidence on Crime Scene) project represents a comprehensive approach to developing HSI capabilities for forensic applications, the French National Research Agency writes. This ambitious project aimed to create a single device capable of visualizing biological traces, fingerprints, drugs, and ballistic residues at crime scenes. The project's scope reflects the technology’s versatility in detecting diverse types of evidence that might be encountered in different types of criminal investigations.

Studies also have explored the detection of residues from explosive manipulation using near-infrared HSI, demonstrating promising results for forensic applications. The technology’s ability to detect trace amounts of materials that might be invisible to conventional detection methods makes it particularly valuable in cases involving improvised explosive devices or sophisticated criminal operations.

Trace Evidence And Pattern Analysis

Recent research has expanded HSI applications to include the analysis of beverage stains, which can provide crucial evidence in certain types of criminal investigations. A comprehensive study examined twelve different beverages and four types of paper towels to create sample stains for analysis, Nature writes. The research demonstrated that HSI could not only detect the presence of various beverage stains but also predict their age, information that could be crucial for establishing timelines in criminal cases.

The study’s methodology involved analyzing spectral data recorded at different time intervals up to 72 hours, tracking how spectral characteristics changed as stains aged. This temporal analysis capability is particularly valuable in cases involving poisoning, sexual assault facilitated by drink tampering, or robbery cases where beverages were used to incapacitate victims. The research employed support vector machine classification models and convolutional auto-encoders for data analysis, demonstrating high accuracy rates in beverage identification and age estimation.

HSI also has been integrated into comprehensive crime scene documentation systems, providing capabilities beyond traditional photography. Research has explored photogrammetry using visible, infrared, hyperspectral, and thermal imaging for complete crime scene analysis.

This multi-spectral approach enables investigators to capture evidence that might be missed by conventional documentation methods, providing a more complete picture of crime scene conditions and evidence distribution.

The technology’s ability to reveal invisible biological traces has been demonstrated through near-infrared chemical imaging studies that can locate semen, vaginal fluid, and urine in stained evidence. This capability is particularly valuable in sexual assault cases where biological evidence might be present but not visible to the naked eye or conventional photography.

Limitations And Future Developments

While HSI shows tremendous promise in forensic applications, several challenges remain in its widespread implementation. Environmental factors such as temperature and humidity can affect spectral measurements, requiring careful control of imaging conditions to maintain accuracy, writes the National Center for Biotechnology Information. Additionally, the technology currently requires specialized training for operators and sophisticated data analysis capabilities that may not be readily available in all forensic laboratories.

The cost and complexity of HSI systems also present barriers to widespread adoption, though technological advances are gradually making the technology more accessible. Current research focuses on developing more portable, user-friendly systems that can be deployed effectively in field conditions while maintaining the accuracy and reliability required for forensic applications.

Future developments are likely to focus on expanding the range of detectable substances and improving the speed and accuracy of analysis. Integration with artificial intelligence and machine learning algorithms promises to enhance the technology's analytical capabilities, potentially enabling real-time analysis and automated evidence identification at crime scenes.

A Transformative Technology

HSI represents a transformative technology for forensic investigations, offering non-destructive, highly sensitive analysis capabilities across a wide range of evidence types. While many applications remain in the research and development phase, demonstrated capabilities in bloodstain analysis, fingerprint detection, gunshot residue examination, and trace evidence analysis show significant promise for solving complex criminal cases.

The technology's ability to preserve evidence integrity while providing detailed spectral information makes it particularly valuable for cases requiring multiple analytical approaches. As the technology continues to mature and become more accessible, HSI is likely to become an increasingly important tool in the forensic investigator’s arsenal, potentially revolutionizing how crime scenes are analyzed and evidence is processed.

The ongoing research and development efforts suggest that future forensic investigations will benefit from even more sophisticated and versatile HSI capabilities, contributing to more accurate and efficient criminal justice outcomes.