Kathmandu, June 20 The Central Police Forensic Science Laboratory has developed ‘Guidelines for Collection and Preservation of DNA Evidence’ to establish uniform procedures and guidelines for collection and preservation of DNA evidence. The procedures and guidelines outlined in this Standard Operating Procedure are applicable to all scene of crime officers, investigating officers, and medical doctors who are responsible for collecting and preserving DNA evidence in the course of crime investigation. According to the guidelines published by the Samakhusi-based lab, the advent of DNA technology has revolutionised the field of criminal investigation as DNA evidence provides conclusive evidence in cases such as homicide, sexual assault, missing person identification and mass disaster, among others. “However, the success of DNA profiling result depends on the condition of evidence. Improper collection, packaging and preservation of these evidences render downstream analysis by the scientist useless. All biological evidence is subject to deterioration due to microbial growth and environmental conditions. Careful collection and storage will ensure that this evidence is preserved so that useful information can be obtained from its analysis,” the guidelines read. According to the guidelines, evidence that could be subjected to DNA analysis is generally limited to substances that are biological in nature. Blood and bloodstains, semen and seminal stains, tissues and cells, bones and organs, hairs with follicles and saliva include the biological materials from which DNA has been successfully isolated and analysed. “Always wear disposable gloves and mask before touching any evidence. Change gloves between handling different items. Use disposable instruments or clean them thoroughly with 70 per cent alcohol or distilled water before and after handling each sample. Dry the instrument with paper tissue between uses. Avoid talking, sneezing and coughing over evidence. Each item should be packaged, sealed, and labeled as soon as it is taken,” read the anti-contamination measures of the guidelines. In case of mass disasters, accidents, burnt or mutilated bodies, two to three tissues like deep muscle tissue, skin, or other least affected tissue (about 5g) should be collected during autopsy in clean and sterilised containers and be transported in refrigerated condition. Similarly, a standard rape kit must be used to collect vaginal, oral and anal evidence as necessary when it comes to sample collection from sexual offence victims, the guidelines read.