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Sterilization of tools -

Before any evidence collection begins, all tools used—ranging from tweezers to scalpels—must undergo a sterilization process. Sterilization prevents the introduction of foreign DNA or contaminants to the evidence, ensuring that the samples remain pure and uncontaminated from the point of collection through analysis.

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Glove changing -

Investigators wear gloves to protect themselves and preserve the integrity of the evidence. Changing gloves between handling different evidence samples is crucial to prevent cross-contamination. For example, after collecting a blood sample and before moving to collect a hair fiber, an investigator would change gloves to ensure no transfer of material occurs between the two pieces of evidence. 

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Collection in original state -

Collecting evidence in its original, untouched state is paramount for accurate forensic analysis. This means collecting items or samples without altering their position, condition, or composition. For instance, if a firearm is found, it is photographed in situ, and its position and condition are meticulously documented before it is handled and collected. 

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Packaging fragile evidence -

Fragile evidence, such as glass fragments, delicate fabrics, or decomposing materials, requires special handling and packaging techniques to prevent loss or further damage. 

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Visual collection of hairs and fibers -

This technique involves the direct visual inspection of surfaces for hairs and fibers, which can be significant in linking suspects or victims to crime scenes. Investigators use clean forceps and special trace evidence paper to collect these items. 

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Visual collection of hairs and fibers -

This method ensures that the evidence is not contaminated by the collector's hands or tools, maintaining the integrity of the sample for forensic analysis.

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Scraping for sample collection -

For solid samples adhering to surfaces, a clean razor blade or scalpel is used to gently scrape the material into clean paper or directly into a collection container. This technique is often used for collecting dried paint, gunshot residue, or dried biological samples from non-porous surfaces. The scraping must be done carefully to collect enough material for analysis while minimizing damage to the underlying surface.

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Tape lifting for hairs and fibers -

Special tapes that are either water or methanol-soluble are used to collect fine hairs and fibers from various surfaces. This method is particularly useful for collecting evidence from clothing, upholstery, or other fabrics where hairs and fibers can adhere. After application, the tape is carefully removed and placed on a clear piece of acetate or similar material for submission to the forensic laboratory. This technique minimizes damage to delicate evidence and allows for the collection of materials that might be difficult to pick up with forceps.

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Tape lifting for dried blood -

For dried blood stains on non-absorbent surfaces, fingerprint lifting tape is an effective collection method. The tape is carefully applied to the stain and then lifted, transferring the blood to the tape. This non-invasive technique preserves the pattern and distribution of the stain, which can be crucial for bloodstain pattern analysis. The tape is then placed on a clear backing and labeled for submission to the forensic laboratory

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Secure tape on acetate for transport -

For evidence collected using tape lifting, such as dried blood or trace fibers, the tape is then affixed to a clear acetate sheet. This process preserves the collected material's integrity and allows for easy examination under a microscope without directly handling the tape. The acetate sheet is labeled and packaged for submission to the forensic laboratory, ensuring that the evidence remains uncontaminated during transport.

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Vacuuming for trace evidence -

A vacuum equipped with a filtered trap is used to collect trace evidence from larger areas or surfaces where direct collection is impractical. This method is effective for gathering hairs, fibers, and other particulates from floors, seats, or even large pieces of clothing. 

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Filtered trap vacuuming -

This trap is specifically designed to collect and contain evidence while allowing air to pass through. After vacuuming, the contents of the trap are transferred to a clean container, typically made of paper, for submission to the forensic laboratory. The vacuum and trap are thoroughly cleaned between uses to prevent cross-contamination.

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Buccal Swab Collection -

Buccal swabs involve collecting cells from the inner cheek of an individual using a sterile swab. This non-invasive method is standard practice for obtaining DNA samples from suspects, victims, or anyone else who may need to be excluded from the investigation. The collected cells provide a rich source of DNA, which can then be compared to evidence collected at the crime scene. Proper technique, including the use of gloves and avoiding contamination of the swab, is essential for ensuring the viability of the sample.

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Collection of liquid blood samples -

For obtaining liquid blood samples, specially designed vacuum tubes containing EDTA (a preservative and anticoagulant) are used. This method is typically employed in controlled environments, such as hospitals or police stations, where blood can be drawn by a medical professional. The EDTA prevents the blood from clotting, preserving the sample for later DNA analysis. These samples are crucial for establishing definitive DNA profiles of individuals involved in a case.

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Cutting technique for fluids -

When collecting fluid samples from fabrics or other materials, a sterile cutting device is used to excise a section of the material containing the fluid. This technique ensures that the entirety of the stain is preserved for analysis, capturing all potential biological material present. The cut section is then packaged appropriately, often in breathable paper to allow further drying and to prevent microbial growth.

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Wet absorption method -

This method involves using a sterile swab, gauze pad, or threads slightly moistened with sterile distilled water or saline solution to collect liquid samples. The moisture helps to absorb the sample more effectively, particularly useful for dried biological fluids. The swab or pad is then allowed to air dry in a controlled environment before packaging, preserving the biological material for DNA analysis.

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Sterile distilled water use -

For techniques like the wet absorption method, sterile distilled water is used to moisten swabs or pads. This ensures that the collection medium does not introduce any contaminants to the sample. The sterile water helps to mobilize cells or substances on surfaces, making them easier to collect. This technique is particularly useful for collecting trace amounts of biological material from non-porous surfaces or objects.

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Air drying of wet absorbed samples -

Samples collected using the wet absorption method must be air-dried in a controlled environment to prevent the growth of mold or bacteria, which could degrade the sample. This drying process is critical for maintaining the sample's integrity for DNA analysis. The environment for drying should be clean, well-ventilated, and free from potential contaminants.

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Secondary dry swabbing -

After using a moistened swab to collect a sample, a secondary, dry swab is employed to ensure any remaining biological material is absorbed. This technique is especially useful for biological samples where the first swab may not collect all the material. The dry swab can pick up residues that the wet swab did not, ensuring a more comprehensive collection. Both swabs are then submitted for analysis, providing a thorough sample for the laboratory.

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Use of substrate controls -

Substrate controls involve collecting samples from the area surrounding the evidence without the evidence itself. These control samples help forensic analysts identify potential contaminants and understand the environmental context of the evidence. For example, swabbing an area next to a bloodstain allows analysts to determine if chemicals or residues present might interfere with DNA analysis. 

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Drying biological evidence -

Before packaging, biological evidence (such as blood, bodily fluids, or tissues) must be thoroughly dried. This step is vital to prevent the growth of mold and bacteria, which can degrade the DNA in the sample and potentially ruin it for forensic analysis. Drying must be done in a controlled environment to avoid contamination with other samples or environmental contaminants.

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Paper packaging -

Once dried, biological evidence is preferably packaged in paper rather than plastic. Paper allows the evidence to "breathe," reducing the likelihood of condensation and subsequent mold growth. 

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Paper packaging -

This packaging method is especially important for evidence that might be stored for an extended period before analysis. Each package is carefully labeled with the case number, description of the contents, and the date of collection.

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Plastic packaging for dried samples -

In instances where plastic packaging is used (for example, for very small samples or when specific environmental conditions need to be maintained), the sample must be completely dried to prevent moisture buildup. Plastic can create a sealed environment that might promote degradation if any moisture is present. This method requires meticulous attention to the drying process to ensure the sample's integrity is maintained.

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Documentation and refrigeration of liquid samples -

Liquid samples, like water from a crime scene or biological fluids that need to be preserved in liquid form, are documented with detailed labels and packaged in sterile glass or plastic containers. These samples are then refrigerated as soon as possible to slow down any biological processes that could alter the sample. Proper documentation includes the sample's source, the date and time of collection, and any chain of custody transfers to ensure the evidence is accurately tracked throughout the investigation.

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Consultation with department SOPs (Standard Operating Procedures) -

Investigators consult their department's SOPs regarding evidence collection, packaging, and preservation. These SOPs provide a framework that ensures consistency, reliability, and adherence to legal standards across all investigations. Regular consultation and adherence to these procedures ensure that evidence collection methods are up-to-date and follow best practices.

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Consultation with forensic labs -

Before collecting evidence, investigators often consult with forensic laboratories to understand specific requirements for evidence preservation and packaging. This consultation ensures that evidence is collected in a manner that aligns with the laboratory's analysis protocols, reducing the risk of sample degradation or contamination and increasing the likelihood of obtaining reliable, actionable forensic results.

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Elimination and comparative analysis -

Reference samples are collected from individuals potentially linked to the crime scene, such as suspects, victims, and witnesses. These samples are crucial for elimination purposes or comparative DNA analysis. By comparing these known samples to evidence collected at the scene, investigators can confirm or exclude individuals' involvement in the crime, providing a powerful tool in the investigative process.

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Ethical considerations in evidence collection -

Ethical considerations are paramount in crime scene investigation, especially when collecting sensitive evidence such as biological samples. Investigators must respect privacy rights and obtain necessary consents or warrants. Ethical practices also extend to how evidence is handled, stored, and analyzed, ensuring that all investigative actions are justifiable and respectful of all individuals involved.

Sources: (All About Forensic Science)

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