criminalistics

Forensic science

Broad application of science to legal questions

Criminalistics

scientific examination and interpretation of physical evidence

Orfila

toxicology

Bertillion

anthropometry

Galton

fingerprints

Lattes

blood grouping

Goddard

firearms

Osborn

questioned documents

Locard

exchange principle

Transferred material can occur by

• person to person

• person to broken window

• footwear to ground

• vehicle to vehicle/object

• tool to surface

Physical Science / Chemistry evidence

drugs, glass, paint, soil, unknown materials

Biology / DNA evidence

Blood, saliva, semen, tissue, other biological material |

Firearms / Toolmarks

firearms, bullets, cartridge cases, tools, marked surfaces

Questioned Documents

handwriting, signatures, printed documents, altered documents

Trace Evidence

Hair, fibers, glass, paint, small transferred materials

locard’s principle of exchange

whenever two objects come into contact, there is a mutual exchange of materials between them

Forensic pathology

cause and manner of death through medical examination and autopsy

Forensic anthropology

skeletal biology and anthropology

Forensic entomology

insects

Forensic psychiatry / psychology

behavioral and mental-health expertise to legal questions.

Physical evidence

Tangible material that can provide information about an investigated event.

What is the primary role of a crime laboratory?

to apply scientific methods and techniques to examine, process, and analyze physical evidence collected from crime scenes to assist law enforcement

crime lab units

• physical science/trace evidence

• biology/DNA

• drug chem/controlled substances

• toxicology

• firearms/toolmarks

• latent prints

FBI

Provides broad forensic capabilities and specialized examinations supporting federal investigations and, in appropriate circumstances, other agencies

DEA

its laboratory system is strongly associated with analysis of controlled substances and related drug evidence.

ATF

Provides forensic services related to its mission, including areas involving firearms and explosives

U.S. Postal Inspection Service

provides forensic support for investigations involving the U.S. mail and postal system, including document and other evidence examinations

questioned sample

material whose source, identity, or characteristics are under examination

Known/reference sample

material of known origin used

Suspected erasure

oblique light

hidden writing

IR/UV

indented impressions

oblique light, ESDA

different inks

microspectrophotometry, TLC

Questioned documents

A questioned document is any item whose authenticity, origin, or contents are disputed. Examples include letters, checks, contracts, wills, passports, receipts, and writing on nonpaper surfaces.

natural variation

a person never reproduces the same handwriting

Loops (most common)

One or more ridges enter from one side, recurve, and exit on the same side  One delta and a core  

Whorls (medium)

Usually rounded or spiral-like ridge flow  At least two deltas  Four textbook groups: plain, central pocket loop, double loop, accidental

arches (rarest)

Ridges enter one side and exit the other  Plain arch: gentle rise or wave in center  Tented arch: sharp upthrust or steep central rise  Generally no core, delta, or type lines in the basic arch pattern.

Refractive index

 Compares optical behavior using immersion/match point

Becke line visible

refractive indices differ

Becke line disappears

match point.