Guided forensic dossier Forensic DNA Evidence Review
01 / 09 · Case entry
Decision trail:
Case entry

Forensic DNA Evidence Review

Review draft report statements against the evidence file. Approve what can move forward, revise what is premature, and reject what cannot be defended. Your decisions build the final report.

Forensic DNA data collage
Evidence intake

Reference material documented.

A buccal swabCells collected from the inner cheek. Used as a known reference sample for DNA comparison. reference sample is available for comparison.

Evidence kit with buccal swab
Item 12. Buccal swab reference sample. Case ID 23-0715-AX.
Chain of custody

Handling record reviewed.

The chain of custodyA chronological record of who handled evidence, when, and why. Gaps can raise admissibility questions in court. log must be intact before the item moves to analysis.

📋
Evidence handling log Item 03 — Case 23-0715-AX
Date / Time
Action
Handler
Status
2023-09-04 08:12
Collected at scene
Det. Morales
OK
2023-09-04 09:45
Transferred to evidence room
Off. Reyes
OK
2023-09-06 —
Transfer to lab (no time logged)
—
Gap
2023-09-06 14:30
Received at forensic lab
Analyst Cho
Note
2023-09-07 09:00
Selected for DNA extraction
Analyst Cho
OK

A transfer entry on 2023-09-06 is missing a timestamp and handler signature. The item was received at the lab later that day, but the gap in the log is unaccounted for.

Evidence review

Marked area on garment.

Item 03 shows a selected area on the inner lining.

Garment with selected area
Item 03. Garment submitted for biological evidence review.
Selected area

Close-up documented.

The selected area was photographed with scale and case metadata.

Close-up of selected stain area
Close-up. Stain area with measurement and item metadata.
Analytical result

D21S11 readout.

The chart displays the alleleA variant form of a gene at a specific locus. In STR typing, alleles are identified by the number of repeat units. calls for one STR locusShort Tandem Repeat — a region of DNA where a short sequence repeats. The number of repeats varies between individuals and is used for identification..

STR chart for D21S11
D21S11. STR readout with allele labels above the peaks.
Mixture analysis

Two contributors detected.

The electropherogramA graph of DNA fragment sizes and signal intensity produced during capillary electrophoresis. Peak height reflects the amount of DNA at each allele. at locus D8S1179 shows four peaks — consistent with a two-person mixture.

0 2000 4000 6000 RFU 13 14 15 16 Major contributor Minor contributor LOCUS: D8S1179
D8S1179 — mixture profile. Four peaks identified. Alleles 13 and 15 are at significantly higher signal intensity than alleles 14 and 16, consistent with a two-person mixture with unequal contribution.
Profile comparison

Profiles compared.

The evidence profile and reference profile are shown across multiple STR lociMultiple STR sites examined together. The combined probability of a random match across all loci is the basis for the statistical weight reported..

Forensic DNA profile comparison table
Comparison table. Evidence profile and reference profile across the loci shown.
Report wording

Statistical weight reviewed.

The likelihood ratioA number expressing how much more probable the evidence is under one hypothesis (e.g., suspect is the source) than another (e.g., a random person is the source). is available for final reporting language.

Likelihood ratio and strength of evidence infographic
Statistical weight. Likelihood ratio and strength-of-evidence scale.
Review complete

Defensible report language

Expert language · each statement reviewed
Review trail
0Accepted
0Flagged
0Removed
0Needs context
Chain of custody Gaps in the handling record must be noted, not omitted. A missing timestamp is a defensibility issue, not a trivial detail.
Mixture profiles A multi-peak electropherogram cannot be summarized as a single-source match without probabilistic analysis.
Guilt language DNA evidence informs strength of inclusion. Commission of a crime is a legal conclusion — never a laboratory finding.
Analyst notes card
Learning design sample by Walkelia Fabián, MD.
This is a learning design sample, not a substitute for accredited forensic science training or legal advice. Real forensic casework requires compliance with laboratory quality systems, jurisdictional standards, and applicable law.
Review basis

Review basis
    Evidence base

    Sources reviewed

    This experience was informed by current forensic DNA interpretation guidance, quality standards, and recent literature on STR analysis, likelihood ratios, sequencing-based mixture data, Rapid DNA, and forensic genetic genealogy.

    Technical guidance and quality standards

    1. Federal Bureau of Investigation. (2025). Rapid DNA. FBI Law Enforcement. https://le.fbi.gov/science-and-lab/biometrics-and-fingerprints/codis/rapid-dna
    2. Scientific Working Group on DNA Analysis Methods. (n.d.). Publications: Interpretation guidelines, likelihood ratios, probabilistic genotyping, validation, and quality assurance standards. SWGDAM. https://www.swgdam.org/publications
    3. Scientific Working Group on DNA Analysis Methods. (2025). FAQ. SWGDAM. https://www.swgdam.org/faq

    Current forensic DNA methods

    1. Gettings, K. B., Bodner, M., Borsuk, L. A., King, J. L., Ballard, D., Parson, W., Benschop, C. C. G., Børsting, C., Budowle, B., Butler, J. M., van der Gaag, K. J., Gill, P., Gusmão, L., Hares, D. R., Hoogenboom, J., Irwin, J., Prieto, L., Schneider, P. M., Vennemann, M., & Phillips, C. (2024). Recommendations of the DNA Commission of the International Society for Forensic Genetics (ISFG) on short tandem repeat sequence nomenclature. Forensic Science International: Genetics, 68, 102946. https://doi.org/10.1016/j.fsigen.2023.102946
    2. Romsos, E. L., Kiesler, K. M., Steffen, C. R., Borsuk, L. A., Riman, S., Mullen, L. E., Irwin, J. A., Vallone, P. M., & Gettings, K. B. (2025). Development of publicly available forensic DNA sequence mixture data. Genes, 16(3), 333. https://doi.org/10.3390/genes16030333
    3. National Institute of Standards and Technology. (n.d.). DNA mixture interpretation. NIST. https://www.nist.gov/node/1876346

    Ethics and investigative use

    1. United States Department of Justice. (2019). Interim policy: Forensic genetic genealogy DNA analysis and searching. U.S. Department of Justice. https://www.justice.gov/d9/pages/attachments/2019/09/24/finaldojinterimpolicyonfgg.pdf