What is the purpose of a crime scene search?
The purpose of a crime scene search is to locate, recognize, and collect physical evidence that can help reconstruct the events of a crime and link a suspect, victim, and crime scene.The goal is to ensure that no potential evidence is overlooked and that all evidence is properly documented and preserved for analysis.
What is a chain of custody?
The chain of custody is the record of who collected, handled, transferred, or analyzed each piece of evidence from the moment it was discovered until it’s presented in court.
(show collectors’ initials, location of evidence, and date of collection)
What types of searches are performed at the scene (line search vs. grid, spiral, etc…)
line/stip: 1-2 Searchers move in straight lines, a little off the boarder and straight across to the other side, best used when boundaries are well established (field, parking lot)
grid: 2 ppl doing a line search on adjacent corners and forming perpendicular lines, boundaries must be established, more thorough than line search
spiral: 1 person moves inward from boundary to center or vice versa- moving from an area light with evidence to an area evidence may most likely be found (easy to find direction of footprints but hard to form perfect spiral-evidence may be missed)
quadrant/zone: Scene is divided into zones, and each is searched separately; ideal for big areas like houses, buildings, or rooms.
wheel/ray: several people starting at a zone and moving outward or vice versa- not preferred as areas between rays are not searched
What is Locard’s Exchange Principle?
whenever two objects come into contact with another there is an exchange between them, “Every contact leaves a trace.” such as hair, fibers, skin cells, or soil — that can link a suspect, victim, and scene.
What is physical evidence?
any object that can establish that a crime has or has not been committed or can link a crime and its victim or its perpetrator (when preformed with a selectively governed by the collectors thorough knowledge of the crime laboratories techniques, capabilities and limitations) (blood, fingerprints, hair, fibers, weapons, bullets, documents, tool marks-measurable)
What are the different types of microscopes and what would they be used for?
compound: most commonly used, Uses two lenses (objective + eyepiece) to magnify small, transparent samples like hair, fibers, or glass fragments.
comparison: (side-by-side comparisons) Two compound microscopes connected side-by-side with a split-view field. Used for comparing bullets, cartridge cases, fibers, or hair samples directly.
Stereoscopic (Dissecting) Microscope: 3d imagae at low magnification (right-side up image) most used, used for examining larger or opaque items like soil, paint chips, or tool marks without having to cut or prepare the sample.
Polarizing Microscope: (like sunglasses) uses polarized light to identify minerals, fibers, or crystals, Often used for soil analysis or man-made fibers.
Microspectrophotometer: Combines a microscope with a spectrophotometer to measure light absorption. Used to analyze dyes, paints, or fibers by their color spectrum.
Scanning Electron Microscope (SEM): Uses a beam of electrons (not light) for very high magnification and depth of field. Used to examine gunshot residue, tool marks, or minute surface details.
What is a SEM-EDX? What is it used for?
scanning Electron Microscope with Energy-Dispersive X-ray analysis.SEM provides detailed surface images of a specimen using electrons.
EDX detects elemental composition by measuring X-rays emitted from the sample when struck by electrons.
➡️ Together, SEM-EDX is used to analyze gunshot residue (GSR), paint, glass fragments, metals, and trace elements — identifying both shape and chemical makeup.
What is a stereoscope? When would you use it?
(or dissecting microscope) gives a three-dimensional view of a specimen at low to medium magnification (about 10×–125×). used for large, opaque objects (paint chips, soil, hair roots, tool marks, documents).
Situations where you don’t need to cut thin sections or shine light through the sample.
➡️ It’s ideal for initial evidence screening before moving to more advanced analysis.
fingerprints: how do they form?
Fingerprints form before birth, during fetal development.
The ridges (called friction ridge skin) form on the fingers, palms, and soles as the skin layers grow.
The pattern is determined by genetics and random pressures in the womb, which means no two people (even identical twins) have the same fingerprints.
➡️ Once formed, they never change, only enlarge as a person grows.
fingerprints: how can they be developed or enhanced?
Physical Methods (powders):
Fingerprint powder (black, white, magnetic, fluorescent) adheres to oils and sweat in a latent print.Used on nonporous surfaces (glass, metal, plastic).
B. Chemical Methods:
Iodine fuming: Reacts with oils and fats; temporary brown print. Ninhydrin: Reacts with amino acids; forms purple-blue prints on paper or cardboard.
Silver nitrate: Reacts with salt in sweat; produces dark prints under UV.
Cyanoacrylate (superglue) fuming: Reacts with moisture; creates white, hard prints on nonporous surfaces like plastic or metal.
C. Alternative Light Sources / Lasers:
Used to enhance faint or fluorescent prints after treatment.
What is the difference between latent, patent, and plastic prints?
latent: Invisible to the naked eye; formed by natural body oils and sweat. Must be developed by powder, chemicals, or light. (Glass, metal, plastic)
Patent print: Visible print left by a substance on the fingers (like blood, ink, dirt). (Bloody print on a wall)
plastic: 3D impression left in a soft material. (Print in clay, wax, soap, or putty)
loop, whorl, and arch classifications
if the loop opens towards the pinky its an ulnar loop, if it opens towards the thumb its a radial loop,
plain whorl and central pocket loop have at least 1 ridge ending that makes it a complete circuit, if an imaginary line drawn b/t 2 deltas touches any sprial ridge its a plain whorl, if no ridge is touched its central pocket, Accidental whorl: Combination of two or more patterns (e.g., loop and whorl) that doesn’t fit another category.
arch:Plain arch: Simple wave pattern; smooth rise in the center.
Tented arch: Sharp upthrust or spike at the center (resembles a tent).
identify parts of pistol
A — Barrel/Muzzle
The barrel is the metal tube the bullet travels through when fired.
The muzzle is the open end of the barrel where the bullet exits.
Inside are lands and grooves (rifling) that impart spin to the bullet.
B — Trigger
When pulled, it releases the hammer or firing pin, which strikes the cartridge primer to ignite the gunpowder.
C — Hammer
Strikes the firing pin (or primer directly, depending on the design) to fire the round.
Must be cocked before firing in some models (single-action).
D — Grip (Handle)
The part held by the shooter’s hand.
Often houses the magazine (which stores cartridges) in semi-automatic pistols.
How are cartridge/shell casings compared? What marks do we look for in a comparison?
Cartridge cases are compared under a comparison microscope to match them to a firearm, Firing pin impression – from the firing pin striking the primer.
Breechface marks – unique microscopic patterns left on the back of the cartridge as it’s forced against the breechblock.
Extractor and ejector marks – left when the cartridge is pulled from and ejected out of the chamber.
Rim or primer shear marks – from the mechanical movement of the weapon.
➡️ These microscopic marks are individual characteristics, unique to a specific firearm.
What chemical/test is used to detect gunpowder?
Common tests for gunshot residue (GSR):
Griess Test → Detects nitrites from burned gunpowder (orange color appears).
Lead residue test / Sodium rhodizonate test → Detects lead from primer or bullet.
SEM-EDX (Scanning Electron Microscope with Energy Dispersive X-ray) → Confirms presence and elements (lead, barium, antimony) in GSR.
How is the entry angle (impact angle) of a bullet determined?
By examining the shape of the bullet hole or trajectory:
A round hole indicates a perpendicular (90°) shot.
An oval or elongated hole indicates an angled entry.
The angle of impact can be measured using trigonometry if the path and surface geometry are known (similar to bloodstain analysis).
➡️ The more elongated the hole, the smaller the impact angle relative to the
firearms: What are Class and Individual characteristics?
class: Features that can be associated with a group, not a single source.(caliber of bullet, number and direction of lands/grooves, rifling pattern.)
individual: Unique microscopic markings produced by random imperfections; identify a specific firearm or tool.(Striations on a bullet, breechface marks, firing pin impressions)
