Dry Stains on Non-Absorbent Surfaces
Collection procedures for dry stains on nonabsorbent surfaces are as follows:
- Submit the entire item, if possible. (Note: If the entire item is submitted and it is a sharp object such as broken glass, it will need to be safely packaged in cardboard and labeled "sharp object enclosed.")
- Use a new or clean scalpel blade to scrape the stains from the surface.
- Collect the flakes onto clean paper and fold the paper in a bindle.
- If the stain is on wood, shave the area of the bloodstain with a new or clean scalpel blade.
- Package each item separately.
- Place sample in a labeled envelope that provides reference information on where the sample was collected.
- Take a control swabbing from unstained areas using a new sterile swab slightly moistened with distilled water. Allow the control swab to air-dry, label and package in paper.
- If determined by your agency protocol, collect the sample with tape using the following procedure:
- Place fingerprint tape (do not touch sticky surface with bare hands) over bloodstain and surrounding negative control area.
- Rub nonsticky side of tape with a pencil eraser or other blunt object. This is to ensure that good contact is made between the stain and the tape.
- Lift the bloodstain like a fingerprint and place the tape on an acetate backing. (Do NOT use a paper backing — paper makes the stain difficult to handle during analysis). The lifting process can be repeated several times on the same stain if necessary.
- Label the stain(s) and package individually in a paper envelope.
Advantages: The dilution and contamination potential is minimized by eliminating the use of water as the collection medium; a control is readily collected; it requires little storage space and is a fairly easy technique to perform.
Disadvantages: Investigator must decide which stains to collect; bloodstains do not lift well off certain surfaces. A potential drawback to this method is possible touch DNA contamination if the investigator repeatedly reaches into a common tape lift bag or handles the sample using nonclean techniques.
Additional Online Courses
- What Every First Responding Officer Should Know About DNA Evidence
- Collecting DNA Evidence at Property Crime Scenes
- DNA – A Prosecutor’s Practice Notebook
- Crime Scene and DNA Basics
- Laboratory Safety Programs
- DNA Amplification
- Population Genetics and Statistics
- Non-STR DNA Markers: SNPs, Y-STRs, LCN and mtDNA
- Firearms Examiner Training
- Forensic DNA Education for Law Enforcement Decisionmakers
- What Every Investigator and Evidence Technician Should Know About DNA Evidence
- Principles of Forensic DNA for Officers of the Court
- Law 101: Legal Guide for the Forensic Expert
- Laboratory Orientation and Testing of Body Fluids and Tissues
- DNA Extraction and Quantitation
- STR Data Analysis and Interpretation
- Communication Skills, Report Writing, and Courtroom Testimony
- Español for Law Enforcement
- Amplified DNA Product Separation for Forensic Analysts