How to Properly Swab DNA Evidence at a Crime Scene

Summary

This video provides a detailed guide on the proper collection of biological evidence, specifically bloodstains, at a crime scene. It covers essential practices like correct glove usage to prevent DNA contamination, handling wet and dried bloodstains, and collecting very small stains, all while emphasizing the importance of detailed documentation and appropriate packaging.

Highlights

Introduction to Biological Evidence Collection and Glove Usage00:00:00

The video introduces the topic of biological evidence collection, focusing on blood. It emphasizes the importance of proper glove usage to prevent touch DNA contamination, recommending grabbing gloves from the base and potentially wearing two pairs: one for general tasks and an outer pair for evidence collection.

Collecting Wet Blood Stains00:02:03

For collecting wet bloodstains, the video instructs viewers to first fill out a pre-made swab box with case details, date, time, name, and item number. It stresses using pre-packaged sterile swabs and collecting as much of the sample as possible by twirling the swab, followed by drying the swabs before packaging.

Collecting Dried Blood Stains00:04:54

When collecting dried bloodstains, similar documentation on a swab box is required. The method involves using one to two drops of sterile or distilled water on the swab to rehydrate and collect the dried blood, being careful not to dilute the sample too much. The goal is to concentrate as much blood as possible on the swab.

Collecting Very Small Blood Stains00:07:00

For very small bloodstains, the technique changes to using only one swab with a single drop of water, concentrated at the end of the swab. This method aims to maximize the DNA yield for laboratory analysis, particularly for stains less than a millimeter in size. The video also advises against contaminating the sterile water container when rehydrating the swab.

Packaging and Labeling Evidence00:08:40

After collection, all swabs should be packaged in paper, never plastic, and sealed and labeled correctly. It is crucial to change gloves between collecting each item of evidence to avoid cross-contamination.