CSI Cheat Sheet 2026

The 30 highest-yield CSI facts, distilled from real exam questions. Print it, save it as a PDF, or study it here — free, no sign-up.

1. What is 'Locard's Exchange Principle' as applied to trace evidence analysis? → Every contact leaves a trace between two surfaces
2. A CSI finds a latent print on a knife blade. Which processing sequence is correct? → Photography → cyanoacrylate → fluorescent dye
3. Which of the following should NOT be included in the factual portion of a crime scene report? → Investigator's theory about how the crime occurred
4. What is the significance of 'hesitation wounds' in a forensic death investigation? → They suggest a self-inflicted injury, often seen in suicides
5. An investigator is collecting a firearm at a crime scene. Which of the following actions should be AVOIDED to preserve potential trace evidence and for safety? → Placing a pencil or other object into the barrel to pick it up.
6. What is the purpose of a 'Locard's Exchange Principle' as it relates to a CSI's legal responsibilities? → It establishes that every contact leaves a trace, making contamination a legal concern
7. Which type of report summarizes the findings and details of a crime scene investigation? → Investigative report
8. A decedent is found with cherry-red lividity. Which toxic substance is most likely responsible? → Carbon monoxide poisoning
9. In a fire investigation, what is 'V-pattern' burn evidence used to determine? → The point of fire origin
10. Why is a crime scene sketch important? → To show spatial relationships of evidence
11. Which of the following fluorescent dyes is commonly used after cyanoacrylate fuming to enhance contrast on multi-colored surfaces? → Rhodamine 6G
12. Which doctrine allows evidence found during a lawful search, even if not listed in the warrant, to be admitted in court? → Plain view doctrine
13. What is the primary purpose of crime scene documentation? → To create an accurate record for investigations
14. Which controlled substance color test produces a purple/violet reaction when testing for opiates? → Marquis reagent
15. When photographing a shoe impression in soil at a crime scene, what is the correct oblique lighting angle? → A low angle of approximately 10-45 degrees
16. When casting a tire track impression in soft soil, what material is most commonly used? → Dental stone
17. Which reagent is commonly used to enhance latent fingerprints on porous surfaces such as paper? → Ninhydrin
18. What is 'saponification' in the context of decomposed remains? → Conversion of body fat into a waxy, soap-like substance (adipocere)
19. A CSI is asked to testify as an expert witness. Which statement best describes the CSI's role in this context? → To provide objective scientific opinion within their area of expertise
20. What is the primary reason investigators use an alternate light source (ALS) when searching for biological fluids? → To cause biological fluids to fluoresce or absorb light differently
21. When photographing a footwear impression in mud, which sequence is correct? → Without scale first, then with scale, using oblique lighting for both
22. What information must appear on every evidence label or tag at a crime scene? → Item number, date/time collected, collector's initials, and case number
23. Why should a CSI record the condition of lighting at a crime scene? → Because lighting conditions may affect what was visible to witnesses or suspects
24. A body shows an entry wound with a 'muzzle contusion ring' and soot deposited deep in the wound track. What type of gunshot wound is this? → Hard contact wound
25. The ethical duty to avoid 'advocate science' means a forensic expert should: → Present findings objectively even if they undermine the hiring party's case
26. What does the forensic term 'mechanism of death' refer to? → The physiological derangement by which the cause of death produces the fatal outcome
27. In the ACE-V methodology for fingerprint comparison, what does the 'V' stand for? → Verification
28. When documenting a pooled bloodstain, what measurement is recorded to help reconstruct the event? → The area, shape, and perimeter characteristics of the pool
29. Which type of fracture pattern on glass can indicate the direction of force application? → Radial and concentric fracture patterns
30. What is the main purpose of using a 'fluorescent powder' rather than a standard aluminum or carbon powder? → It provides contrast on multi-colored or patterned backgrounds under UV/ALS