How to collect blood samples from a crime scene? (2023)

How to collect blood samples from a crime scene?

Place thread on bloodstain with a pair of clean forceps or a clean cotton swab. Roll the thread on the bloodstain, so the stain is absorbed onto the thread. Repeat until a minimum of four threads are collected. Place the threads (and swabs, if used) in a secure area and allow them to air dry.

Most blood found at crime scenes is already dried. It can be collected by scraping, if the deposit is crusty or flaky, and stored in a paper fold. Dried blood smears can be collected on moist pieces of cotton cloth or cotton swabs. Blood stained objects can be submitted whole to the lab.

A clean cotton cloth can be used to soak up liquid blood or a blood clot (avoiding areas containing only serum). Wet blood samples, if they are collected, must be preserved in a suitable anticoagulant and kept in a refrigerator. These specimens should be submitted to the laboratory as soon as possible.

Liquid blood evidence is generally collected from blood pools but can be collected off of clothing as well, using a gauze pad or a sterile cotton cloth. Once the sample is collected it must be refrigerated or frozen and brought to the laboratory as quickly as possible.

Collect evidence correctly, preserve each specimen separately, use and change gloves often, avoid coughing or sneezing during the collection, use appropriate tools such as cotton-tipped applicators, sterile water, cardboard swab boxes, separate paper bags, and envelopes to prevent cross-contamination of samples ...

Collection techniques include picking, lifting, scraping, vacuum sweeping, combing and clipping. Several tools can be used for the collection of trace evidence (eg tweezers, tape lifts, spatulas).

Wipe up the spill as much as possible with paper towel or other absorbent material. Gently pour bleach solution – 1 part bleach to 9 parts water – onto all contaminated areas. Let bleach solution remain on contaminated area for 20 minutes and then wipe up remaining bleach solution.

Confirmatory tests for blood include identification of blood cells under a microscope [Shaler, 2002], crystal tests such as the Teichman and Takayama tests [Shaler, 2002; Spalding, 2003], and ultraviolet absorption tests [Gaensslen, 1983].

Analysts or investigators will typically soak up pooled blood, or swab small samples of dried blood in order to determine if it is human blood and then develop a DNA profile. This becomes critical when there are multiple victims.

What are the 7 steps of crime scene investigation?

Dried blood spot specimens are collected by applying a few drops of blood, drawn by lancet from the finger, heel or toe, onto specially manufactured absorbent filter paper. The blood is allowed to thoroughly saturate the paper and is air dried for several hours.

Raman spectroscopy and advanced statistics allow the researchers to date a blood stain accurately, provided said blood stain is less than two years old. Raman spectroscopy involves shining a laser on a sample and measuring the intensity of scattered light.

Tools ​To establish facts and develop evidence, a criminal investigator must use these tools-information, interview, interrogation, and instrumentation.

Liquid blood evidence is generally collected from blood pools but can be collected off of clothing as well, using a gauze pad or a sterile cotton cloth. Once the sample is collected it must be refrigerated or frozen and brought to the laboratory as quickly as possible.

The most site for venipuncture is the antecubital fossa located in the anterior elbow at the fold. This area houses three veins: the cephalic, median cubital, and basilic veins (Figure 1).

Collect drops of blood into the collection tube/device by gentle pressure on the finger. Avoid excessive pressure or “milking” that may squeeze tissue fluid into the drop of blood. Cap, rotate and invert the collection device to mix the blood collected.

The sample is obtained by needle puncture and withdrawn by suction through the needle into a special collection tube. Some specimens may be obtained by a finger puncture that produces a drop of blood, such as that used for glucose testing.