Evaluation of the usefulness of the alternative light source (ALS) in differentiating simulated bloodstains

Abstract

The alternative light source (ALS) is a helpful technique for the detection of biological traces at a crime scene, which allows preservation of the material without destroying it. The aim of this study was to differentiate the human blood from a group of simulated bloodstains, which included: red borscht, raspberry juice, cherry liqueur, cranberry juice, tomato bruschetta, tomato paste, raspberry jam, rust, red spray, red wine and tomato ketchup. Stains, made of different types of material, were illuminated with the ALS emitted by the Mini-CrimeScope 400 (SPEX Forensics) with yellow, dark yellow, orange and red filters. The results of the analysis were presented as a description and also documented in photographs. The usage of light sources without color cut-off filters does not allow us to differentiate unequivocally real bloodstains from the trace evidence imitating or resembling bloodstains. The usage of different color cut-off filters (especially red filter) allowed us to exclude simulated bloodstains made of food and alcohol by using CSS light and light with a wavelength of 535 nm, 515 nm, 455 nm, 415 nm and 300-400 nm. Due to the different optical properties of blood and substances containing vegetable ingredients, forensic experts can differentiate human blood from simulated bloodstains by using the ALS in a non-destructive and quick way already at the crime scene. The ALS may be an example of a method which can replace more commonly used chemical-based screening tests.