Specht, Walter

views updated

Specht, Walter


In 1937, at the University Institute for Legal Medicine and Scientific Criminalistics in Jena, Germany, Walter Specht introduced the use of luminol as a presumptive test for blood at crime scenes. This is forensically important, because perpetrators often wash away visible signs of blood at the scene, in an effort to remove all possible evidence of the crime.

A presumptive test for blood is used when forensic investigators have strong reason to suspect that blood is present but is not currently visible at the scene. A presumptive test will neither prove nor disprove, in and of itself, the presence of blood at a crime sceneit will merely indicate a likelihood, which should then be further investigated.

Forensic scientists use a spray containing luminol and hydrogen peroxide to detect trace blood at crime scenes. Hemoglobin in blood catalyzes the breakdown of hydrogen peroxide into oxygen, which can oxidize the luminol. It works well with both fresh and dry blood, and can be applied several years after the incident. The luminol solution is fine sprayed over the suspected area of a room or object in the room. When sprayed on an area containing blood, luminol produces a chemiluminescent reaction (a glow) instead of color. It is best viewed in total darkness, due to its relatively weak luminescence. The order of use for luminol at a crime scene is: (1) Spray walls first, to illuminate spatter patterns; (2) Spray ceiling next, to highlight cast off patterns; (3) Spray floors, in order to detect shoeprints , drag marks, etc., last. Luminol should only be applied once; additional application will only serve to dilute any blood present.

Luminol is considered highly sensitive: it can detect the presence of blood in a ratio of one part per million (1:1,000,000). In contrast to its high sensitivity, it has a relatively low rate of specificity: in addition to reacting to the presence of blood, it can also react to chemical oxidants such as chlorine bleach, certain types of chemical cleaners, and detergents. Crime scene investigators always follow up a positive presumptive indicator with more specific quantifying tests at the luminol-identified sites.

Among the many benefits of presumptive testing with luminol are its heme-specific sensitivity; its relative stability and lack of toxicity (important due to repeated exposures over time at multiple crime scenes); and its reliable yet inexpensive preparation. Of particular forensic significance is the fact that luminol rarely destroys other evidence (if properly prepared and used) and will not interfere with the future DNA testing of recovered crime scene blood. In addition, presumptive testing with luminol meets the Frye standard for general scientific and legal acceptance.

Because it works well with both fresh and dry blood, and can be applied several years after the incident, luminol is as useful in cold cases as it is in current crime scene investigation . Though originally designed for use in the German copper mining industry as a means of uncovering new sources of ore, Walter Specht's use of luminol in crime scene investigation settings made an enduring contribution to the field of forensic science .

see also Blood spatter; Cast-off blood; Cast-off trails; Cold case; Crime scene cleaning.