Detection and visualization of human tears using alternate light sources for forensic purposes.

The current scientific techniques for locating body fluids focus on quick and effective methodologies for easy and reliable identification. Efficient detection and identification of body fluids play a vital role in establishing the 'corpus delecti' of a crime. Non-destructive techniques such as the use of Alternate Light Sources (ALS) have been exploited for crime scene searches over large areas and detection of body fluids such as blood, semen, vaginal secretions, and saliva on a range of substrates. Tears are rarely found but can be considered as potential body fluid evidence due to their unique biochemical and molecular properties. Tears are secreted in response to physical or emotional stimuli. Due to the small volume of secretions, they are often overlooked in the crime scene. Tears may be found on surfaces such as clothing, bedding, tissue, handkerchief, or balaclava. The use of ALS to locate tears on tissue paper and fabric surfaces was tested which were not apparent to the naked eye. Tears stains were successfully detected on surfaces of forensic interest with varying sample ages up to three months with a broad excitation spectrum between 254 nm and 410 nm. Dried stains on tissue paper and fabric substrates were better detected with sharp margins, clear stain pattern visibility, and fluorescence intensity in comparison with moist and fresh stains. Tears stains can hence be detected with the use of ALS and suitable filter combinations under normal conditions and do not require any specific settings to locate them. These findings are suggestive for easy and quick identification of tears on large surfaces and as a presumptive test for forensic casework evidence examination.

Forensic DNA profiling of tears stains from commonly encountered substrates.

The detection and recovery of body fluid evidence to reconstruct the involvement of people in a crime is an essential step in forensic investigation. The presence of tears is extremely rare but widely misunderstood because of its nature of secretion and low volumes found. They may be secreted in cases of sexual crimes, kidnaping, and violence among many other emotionally disturbing scenarios. It is suggestive that tears are an excellent source of epithelial cells for DNA to establish identity. They are deposited on tissue paper or handkerchief and lesser common substrates include bedding, face mask, and balaclava. Trace or touch DNA can also be retrieved from used contact lenses. Since tears can be secreted due to an emotional response, they can attract forensic analysis for identification. DNA profiling from these substrates is promising in the absence of other commonly found body fluids such as blood or saliva. The current study was done to explore the use of fresh and aged tear samples for forensic DNA analysis from three different substrates i.e., tissue paper, cotton fabric, and contact lenses. STR profiles were successfully obtained from all sample types (n = 60) with 100% allele recovery. The analysis provided consistent evidence that DNA extracted using this methodology was helpful to get reliable DNA profiles for forensics comparable with that from blood or saliva for personal identification.