Infrared Based Imaging and Forensic Applications

Table of Contents

The Night Of….Infrared-Imaging 101Using IR Imaging to Solve CrimesAn Errant Paint Chip can Mean 25 Years to Life…Body Heat: A Criminal's Worst EnemyImmediate Evidence

The Night Of….

January 3rd 2012 was an evening that started out as a jovial evening among friends, but unfortunately turned into a bloodbath. On that fateful day, three men were enjoying a meal around a fire, at a camping area in Sarasota, Florida, when an argument broke out between two of them. Although witnesses in the area instantly called police, unfortunately they were too late. The suspect, wielding a machete, had fled the scene after murdering his friend.

One witness stayed back, and told his version of the evening. However, to figure out exactly what happened Investigators employed infrared imaging. By examining the blood spatter on the clothing of the victim, witnesses and suspects, as well as the environment in which the murder occurred, they eventually figured out exactly how the scene unfolded.

Infrared-Imaging 101

These days, we come across waves (or radiation) from the electromagnetic spectrum in numerous forms. However, the most familiar wave is the 'visible light' which is typically found between UV (ultraviolet) and IR (infrared) wavelengths.

In simple terms, the light that is visible to human eyes dwells between 400 and 700 nanometers. IR light occupies the wavelength between microwave radiation (or the range between 700 and 15,000 nanometers) and visible light, and although it is invisible it is constantly being emitted by objects based on their temperature. While infrared light is invisible to the human eye, it can still be detected by cameras with special sensors that transform the infrared light into a signal which is then shown as an image.

Using IR Imaging to Solve Crimes

Luminol is an organic compound that exhibits a glowing quality, or chemiluminescence, when mixed with the iron found in blood. It is widely used in shows like CSI to expose bloodstains at a crime scene. When luminol is sprayed at a crime scene, blood that is not instantly apparent to the human eye is revealed. Still, it does have its restrictions – it is pretty toxic and is capable of diluting the blood and rendering it useless for DNA testing. As DNA is usually the most critical factor in tying a suspect to a crime scene, the preservation of blood is of major importance.

Crime scene with luminol sprayed to reveal trail of blood.

Latest advancements in infrared photography have ushered in a new era in forensic analysis and crime scene investigation. When an image captured with an infrared sensitive camera is illuminated by an alternate light source, then blood or other trace evidence can be exposed without compromising the crime scene, and can preserve it for additional testing and examination.

Based on what Investigators are searching for, filters can be swapped out on infrared cameras to uncover the evidence that can only be seen with certain parts of the infrared spectrum. For instance, if blood is what they are looking for, they will use a filter coated with albumin, a protein found in both blood plasma and egg whites. Fingerprints, drugs and even explosives can be detected using other filters.

The image on the left depicts a black piece of cloth with no visible stains. The image on the right, taken with an infrared camera, shows a blood stain in the top right corner. (Image courtesy of Scott T. De Broux)

An Errant Paint Chip can Mean 25 Years to Life…

Infrared spectroscopy is an even more comprehensive use of infrared technology in forensics. In other words, infrared spectroscopy involves the use of infrared light to study the chemical bonds within molecules. Every chemical bond within a molecule vibrates at a frequency that is specific to that bond – more or less like a fingerprint. Forensic analysts are thus able to know exactly what a piece of trace evidence is made up of. For instance, they can analyze a paint chip and find out its exact chemical make up and connect it back to the manufacturer, and thus discover what car make it was used on. This can be very helpful for Investigators for example, a hit and run, as it helps them conclude which vehicle the suspect was in.

IR forensics is derived from the fact that all molecules, because of the nonstop motion of their atoms, vibrate at a characteristic frequency which falls within the infrared spectrum. When an individual molecule is struck by an infrared photon that matches its vibrational frequency it will resonate, and this resonance, detected through a variety of spectroscopic techniques, can be used to precisely identify the molecule, much like a fingerprint can be used to identify an individual person.

Lynn Yarris, New Clues from Infrared Forensics

Body Heat: A Criminal's Worst Enemy

Thermal imaging, often confused with infrared¸ is another useful technique that is used in law enforcement.

As mentioned before, all objects discharge a degree of infrared radiation based on their temperature, irrespective of the degree of visible light.

This indicates that it is possible to detect objects, in this case people, in complete darkness. This has shown to be very productive for police monitoring areas at night, and has resulted in the capture of criminals in hiding. This was the case in Baltimore, Maryland where cops caught three armed men hiding after committing an armed robbery. In spite of fleeing the scene, the robbers were caught with the help of a thermal imaging camera that was attached to a roving police helicopter in a nearby forest.

The armed robbers are pictured above hiding in the dense bushes of a forest. Without the thermal imaging camera, they would have been undetectable. (Image courtesy of CBS Baltimore)

It was during the aftermath of the tragic Boston Marathon bombing on April 15th, 2013, where thermal imaging was shown to be very useful. After the police pinpointed the suspect's general location to Watertown, Massachusetts, they used thermal cameras that were fixed to the bottom of a helicopter to identify their exact hiding place on a boat. Although the suspect was hiding under a tarp in the boat, the advanced thermal imaging camera was able to see through it as his body heat was transmissive.

The Massachusetts State Police has released this video showing aerial footage of the boat where Dzhokhar Tsarnaev lay hidden during a standoff with police. (Image courtesy of the Massachusetts State Police)

Infrared Helicopter Video Of Boston Marathon Bomber In Watertown Boat.

Immediate Evidence

In forensic investigations, photography has always been an important tool. In addition, the recent advancements in infrared imaging have expanded its role significantly. The development of live infrared imaging is yet another recent advancement, enabling Investigators to investigate a crime scene with an IR sensitive light source as well as an UV-Vis-IR sensitive camera mounted to a lightweight computer tablet. This in-situ can be used by an Investigator at a crime scene who can then scan the area– collecting evidence on the spot, without having to send the images to a laboratory for analysis. Although this is a relatively new and expensive tool, it could probably become more widespread in the future and also become a vital tool in crime scene analysis.

This information has been sourced, reviewed and adapted from materials provided by Teledyne DALSA.

For more information on this source, please visit Teledyne DALSA.

Source: Infrared Based Imaging and Forensic Applications