Evidence Examination

Irrespective of possible chain of custody rules, examination of evidence starts with photographic and/or drawn descriptions of the items received by the forensic biologist. In every photograph, an absolute scale must be visible (millimeters/centimeters; no pennies, no matches). Resolution should be > 2816 x 2112 pixels=4 MPixel to allow blowing up of the pictures. Flash light should be avoided because brighter parts of the objects will flash out (become white; a digital artefact).

Biological stains that were detected either by their surface properties (detection by touch: e.g., sperm stains on dark clothing), monochromatic light (e.g., saliva), or regular bright light (e.g., hair or small blood stains) are circled and numbered by use of a water-resistant pen or neon color.


Practically all stains can be collected by rubbing them off with a cotton swab. Stains on fabric should be cut out first. Swabs are soaked with one drop of fresh distilled sterile water. After transfer of the stain to the swabs, they must be dried immediately. Then, they are put in paper containers. The most convenient way to dry swabs is to put them straight into a closed cardboard box at room temperature (Fig. 1). There, they can neither touch neighboring objects nor develop mold.[1]

In professional forensic environments, contamination caused by airflow during the drying process has not been reported to be a problem. Some laboratory manuals ask for drying in closed cupboards (Fig. 2) or under sterile laminar airflow. Cupboards must never tightly close to avoid building up of humidity and mold.

Swabbing is performed by intense, multiple rubbing of the stained surface to collect a maximal amount of DNA. Inside of oral cavities, the cotton swab is rubbed against the mucous membrane; saliva alone may not contain enough cells.

After complex shooting situations, used bullets can be matched to the victims by swabbing off traces of tissue that remain on the bullet once it enters the body.[2]

Early Swabbing

Swabbing of clothing items, especially of skin, should be performed as soon as possible in forensic and police investigations. For example, DNA typing was possible in the following cases where swabs had been collected early at the scene of the crime. Before swabbing, intelligent criminalistic assumptions concerning the location of the invisible yet possible stains had been made.

• Epithelial cells of an unknown suspect were swabbed off the front side of a collar of a polo-neck pullover. The victim had been stabbed; the stains had not been visible on the collar.

Fig. 1 Cardboard box allows simple and safe drying and storage of swabs. [Swissforensix, Switzerland (patented).] (View this art in color at www.dekker.com.)

• DNA contained in epithelial cells that had been transferred by saliva of an offender was swabbed off the skin of an experimental victim that had showered. Amplification of the offender's STRs was successful up to several hours after transfer of his saliva to the skin of the victim.

• In contrast to common belief, corneocytes contain DNA. Therefore, all surfaces that may have been touched by an offender (through grabbing of ropes, wearing of baseball caps, hitting a person, inside of gloves) may be swabbed successfully.1-3-5-1

Early swabbing is also necessary whenever cells from the top edge of bottles, beer cans, etc. are collected. Collection of the complete bottle or can frequently leads to spilling of its contents and dilution or washing off the cells. If early swabbing is not possible, the liquid must be drained out of the container by drilling a hole in its bottom.

Filter Paper

Liquid blood can be stored on filter paper that is then dried in the same way as cotton swabs. Filter paper that contains denaturants, buffer, and a free radical trap (e.g., FTA paper[6]) will lyse the blood cells and immediately deactivate bloodborne pathogens such as herpes, cytomegalovirus, and HIV.

Filter paper can also be used to store saliva and liquids from decomposed bodies. In automated laboratories, standard-sized filter paper is the preferred option. Pieces can easily be punched out of it by a machine and subsequently processed by a DNA extraction and PCR robot. The advantage of FTA paper over regular filter paper is that it can be used for multiple PCR reactions. Template DNA will stick to FTA paper after washing off the PCR products and can then be reused.

Urine and Feces

Because feces is found especially at scenes of (serial) burglaries, it should be collected irrespective of its repulsive nature. Fresh feces as well as liquid urine should be frozen below — 20°C to avoid bacterial activity. DNA typing of urine is successful especially if it was excreted in the morning (when the highest number of epithelial cells are found compared to the rest of the day), and from feces after PCR inhibitors are removed. To recover the cells, urine needs to be centrifuged (cells are located in the sediment), whereas stool samples can be extracted straightaway or from swabbings with mini spin columns. The estimated number of up to 6 x 105 pg human DNA/mg stool is never reached in practice because of bacterial and digestive action; nevertheless, up to 170 pg DNA/mg stool were successfully extracted and amplified under case work conditions.1-7,8-1

Fig. 2 Some laboratory standard procedures request cupboards to be used for drying of swabs. Sterile conditions are not necessary; contamination is not a problem as long as the swabs do not touch each other or the wall. Note that the cupboard must not be tightly closed to avoid building up of humidity. (View this art in color at www.dekker.com.)

Fig. 2 Some laboratory standard procedures request cupboards to be used for drying of swabs. Sterile conditions are not necessary; contamination is not a problem as long as the swabs do not touch each other or the wall. Note that the cupboard must not be tightly closed to avoid building up of humidity. (View this art in color at www.dekker.com.)

Fig. 3 Sexual assault kit (University of Bern/Swissforensix, Switzerland): Standardized descriptions and checklists are printed on the actual envelopes that contain the collection materials. (View this art in color at www.dekker.com.)

Sexual Assault Kits

After sexual assaults, biological stains are often collected in a hospital environment, at home, at a general practitioner's office, or at a police station. To avoid contamination of the samples and to allow full collection following a checklist, sexual assault kits are available. Their use is generally and strongly recommended to guarantee collection of all stains in the best possible way even under highly stressful conditions or in cases where lay personnel has to collect the evidence. The kits consist of prepacked envelopes in a cardboard box, which can be stored and stacked at room temperature (e.g., Sexual Assault Care Kit, University of Bern/ Swissforensix, Fig. 3). The envelopes contain swabs, combs for hair (head and pubic), filter paper, sterile distilled water ampoules, large paper bags, and standardized protocol sheets.[1]

Skin Line Prints ("Fingerprints")

DNA is resistant against many histological stains, including substances used to develop fingerprints (or other skin lines). DNA typing was successful from developed skin line prints after cyanoacrylate (super glue fume) or color reagents such as amido black, leucomalachite green, Hungarian Red, DFO, or luminol had been applied.[9,10]

Developed skin line prints should first be documented with a high-resolution camera (5-12 megapixels) or scanner (1200 dpi minimum). The original skin line prints can then be submitted to DNA storage and extraction like any other biological stain. The stronger the initial fingerprint, the more likely a DNA profile may be obtained.

Getting Started With Dumbbells

Getting Started With Dumbbells

The use of dumbbells gives you a much more comprehensive strengthening effect because the workout engages your stabilizer muscles, in addition to the muscle you may be pin-pointing. Without all of the belts and artificial stabilizers of a machine, you also engage your core muscles, which are your body's natural stabilizers.

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