Four different bloodstains on a black T-shirt, made visible using MA-XRF on the basis of the iron and potassium signal. (Credit: Delft University of Technology)

A technology called scanning macro x-ray fluorescence spectroscopy, or MA-XRF, has made impressive breakthroughs in scanning famous artworks, penetrating beneath the layers of paint to find the first strokes and sketches of masters such as Rembrandt van Rijn.

It turns out that the penetrating imaging tool can also detect forensic traces such as body fluids and gunshot residue, a Dutch team of scientists reports this week in the journal Scientific Reports.

“This study clearly shows the potential of MA-XRF imaging for forensic science,” they write. “Benefits of XRF imaging in criminal investigations include the unique elemental contrast to detect and image trace patterns, the non-invasive nature of the imaging and the possibility of depth profiling which can reveal concealed evidence.”

The tools were the M4 Tornado and M6 Jetstream both made by the company Bruker.

The body fluid tests involved depositing samples donated by workers from the Netherland Forensic Institute who were involved in the work. The blood, saliva, sweat, urine and semen were applied to various articles of clothing including black T-shirts, pieces of white cotton and a pair of panties. (For the panties, the mix of semen and urine was intended to mimic the evidence found at the scene of a sexual assault.) Blood stain patterns were deposited to resemble the drip of a bloody nose, a fingermark, expirated blood and a specific impact pattern.

They found the traces imaged well—especially on the items that were too dark or too fluorescent to show up well for evidentiary purposes, they report. Blood shows up through the chemical signatures of potassium, chlorine and iron. Semen shows up through potassium, chlorine and zinc. Saliva is shown mostly through potassium. And urine and sweat show potassium, chlorine and calcium, they explain.

MA XRF elemental scans of female underwear containing a semen and urine stain applied under controlled conditions. (Credit: Delft University of Technology)

Some limitations existed, especially since calcium can be deposited by incidental contact through spilled food and drinks, cosmetics, and work materials like grease, paint or inks.

But overall, the fluids detections proved to guide investigators, they conclude. The X-rays also did not affect DNA samples deposited on the materials, they added.

“Although elementary sensitivity and fabric background levels vary, the results clearly illustrate how MA-XRF imaging can assist in detecting biological traces and direct sampling for further analysis such as DNA STR profiling,” they write. “Additionally, the elemental images are of sufficient quality to forensically interpret patterns and spatial locations of the biological stains to assist in reconstruction and to test witness, victim and suspect statements.”

The gunshot residue utilized test firing at the Netherlands Forensic Institute firing range, involving two handguns, a Makarov 1983 and a Glock 17, with three different kinds of ammunition. The shots were fired into the target clothing at different angles, and at distances from 2.45 to 150 centimeters. The scientists compiled a grouping of key elements: lead, barium, strontium, potassium and chlorine. Together, they could show different types of ammunition—and even the order with which bullets struck their intended targets, they add.

“The full and non-invasive elemental mapping of intact pieces of clothing allows for a detailed shooting incident reconstruction linking firearms and ammunition to point of impact and providing information on the shooting angle,” they write.

“In high-resolution mode MA-XRF can even be used to provide information on the shooting order of different ammunition types,” they add.

The authors conclude that the method would be ideal to locate otherwise invisible aged traces, mixed stains, traces that have poor quality for detection—and also that evidence which has been accidentally or intentionally concealed.

“Such cases include locations were violent crimes including murders and manslaughter have taken place, after which the perpetrators have removed the bodies of the victims and have attempted to remove the evidence by cleaning and redecoration,” they write. “For these special cases, application of MA-XRF at the crime scene could be valuable as it allows scene of crime officers to non-invasively scan areas for hidden forensic traces when the X-rays sufficiently penetrate the surface.”