Luminol is a chemical compound known for its blue-white glow, a phenomenon called chemiluminescence. In forensic science, this property makes it a tool for crime scene investigators. It detects trace amounts of blood invisible to the unaided eye, uncovering hidden evidence and aiding crime scene reconstruction.
The Dawn of Luminol
Luminol was first synthesized in Germany in 1902 by Aloys J. Schmitz. Its light-emitting capabilities were not fully understood at the time. In 1927, W. Lommel reported observing blue chemiluminescence when the compound was oxidized in an alkaline solution.
In 1928, H. O. Albrecht further reported luminol emitting blue light when reacting with oxidants like hydrogen peroxide under alkaline conditions. This was a significant step in understanding its chemiluminescent properties. The compound was officially named luminol in 1934.
From Laboratory to Crime Scene
Luminol’s potential for detecting blood gained recognition after its chemiluminescent properties were observed. By 1936, researchers noted it emitted light when reacting with blood. This laid the groundwork for its application in criminal investigations.
In 1937, German forensic scientist Walter Specht formally proposed luminol’s use for blood detection. Specht demonstrated luminol’s ability to react with blood and produce luminescence, even on various surfaces and after weeks of environmental exposure. His research showed it could reveal bloodstains on materials like stone walls, bushes, and iron pipes, establishing its theoretical forensic utility.
Pioneering Forensic Applications
Following Specht’s work, early practical demonstrations of luminol in a forensic context emerged. In 1937, Specht sprayed a luminol reagent mixture onto blood-stained areas, including those exposed to the elements for 14 days. He found blood-stained regions glowed blue for 10 to 15 minutes, allowing photographic documentation. This demonstrated its effectiveness in revealing aged and weathered bloodstains.
In 1939, San Francisco pathologists Frederick Proescher and A. M. Moody verified Specht’s findings using similar spray mixtures. They detected bloodstains on paper, fabrics, and iron pipes exposed to the elements for three years. Their observations indicated dried and decomposed blood often produced a stronger, more lasting luminol reaction than fresh blood.
Establishing its Place in Forensics
Luminol gradually became an adopted tool in forensic science, integrated into standard police and forensic laboratory procedures throughout the mid-to-late 20th century. Its ability to reveal latent bloodstains, even if cleaned or invisible, solidified its role in crime scene investigations. The compound reacts with iron in hemoglobin (a blood component), producing a blue glow.
This sensitivity allows it to detect minute traces of blood, often diluted to one part per million, making it useful for reconstructing crime scenes where evidence removal was attempted. While it does not differentiate between human and animal blood and can react with other substances like bleach, its effectiveness in visualizing hidden blood patterns has made it a global technique. Its widespread use is also attributed to its high sensitivity, convenience, and non-destructive nature for subsequent DNA analysis.