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

Introduction: 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. Methods: 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. Results: 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. Discussion: 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.