Optical profilometry for forensic bloodstain imaging

Understanding the physical, chemical and biological changes that occur during the drying of a bloodstain is important in many aspects of forensic science including bloodstain pattern analysis and time since deposition estimation. This research assesses the use of optical profilometry to analyze changes in the surface morphology of degrading bloodstains created using three different volumes (4, 11, and 20 μL) up to 4 weeks after deposition. We analyzed six surface characteristics, including surface average roughness, kurtosis, skewness, maximum height, number of cracks and pits, and height distributions from the topographical scans obtained from bloodstains. Full and partial optical profiles were obtained to examine long-term (minimum of 1.5-h intervals) and short-term (5-min intervals) changes. The majority of the changes in surface characteristics occurred within the first 35 min after bloodstain deposition, in agreement with current research in bloodstain drying. Optical profilometry is a nondestructive and efficient method to obtain surface profiles of bloodstains, and can be integrated easily into additional research workflows including but not limited to time since deposition estimation. Optical profilometry is a non-contact tool to scan bloodstains in ambient conditions Drying phases are observable in small drip bloodstains Significant surface morphology changes occur within 35 min after deposition.