Forensics Unit 1

Forensics Science

The application of science to criminal and civil laws

Specific Applications of Forensic Science

• Fingerprints 

• Firearms

• Computer analysis

• DNA

• Drugs

• Trace evidence

Objective Evidence

Science, not influenced by personal feelings or opinions in considering and representing facts → DNA, fingerprints, trace evidence (NOT PERFECT)

Subjective evidance

based on or influenced by personal feelings, tastes, or opinions  → eye witness, confessions etc. 

Lochard’s Exchange Principle

Whenever two objects come into contact with one another, materials are exchanged between them

Observations vs. Perceptions

Obs: What you actually see and cannot be confused with perceptions

Per: What you think about what you saw

Steps of memory

Information from our senses → What we pay attention to → perception → short-term memory → long term memory 

Memory fades with time 

Crime Lab and Units

There is not a national system of crime labs - there are state, city, country crime labs etc.

Units:

• Physical Science Unit

• Biology Unit

• Firearms Unit 

• Document Examination Unit

• Chemistry Unit

•  Toxicology Unit

• Latent Fingerprint Unit

• Crime Scene Investigations Unit

• Computer Unit

Physical Science Unit

Identifies and Compares Trace Evidence 

Biology Unit

investigates anything with DNA (blood samples, body fluids, hair) 

Firearms Unit

investigates discharged bullets, cartridge cases, shotgun shells, and ammunition

Document Examination Unit

provides the skills needed for handwriting analysis and other questioned (document issues - fraud)

Chemistry Unit

identifies illegal substances

Toxicology Unit

examines body fluids and organs for the presence of drugs and poisons.

Latent Fingerprint Unit

processes and examines evidence for latent fingerprints 

Crime Scene Investigations Unit

dispatches specially trained personnel to the crime scene to collect and preserve physical evidence

Computer Unit

analyzes digital data to confirm alibis, find evidence, etc. (cell phone, computers) 

Skills of a forensic scientist

1. Record observations 

2. Conduct test/experience 

3. Analyze results 

4. Write report 

5. Testify in court 

Criminal Law

Could be jail time (like stealing something or killing someone)

Civil law

Don’t go to jail (like traffic violations)

Burden of proof

obligation to provide enough evidence for the jury to reach near certainty, leaving no reasonable doubt of the defendant's guilt

Levels of required proof

• Reasonable suspicion → the amount of evidence that officer need “frisk” someone 

• Probable cause → the amount of evidence that an officer needs to arrest someone 

• Preponderance → Guilty in a civil case 

• Clever and convincing → the amount of evidence necessary for the State to take a child away from parent 

• Beyond a reasonable doubt → Evidence beyond any doubt based on a reason. Guilty in a criminal case 

Evidence admissibility standards (Frye)

• 1923

• general acceptance

• is the scientific method or technique swifting established

Evidence admissibility standards (Daubert)

• 1993

• judge is the gatekeeper

• maryland

• judge reviews if “good science”

• impericle testing

forensics science begins at the

crime scene

Evidence must be

1. observed

2. recorded

3. preserved

crime scen techs will

1. search the crime scene

2. take crime scene notes

3. create a rough sketch of the crime scne

4. photograph crime scene

5. collect evidence

Crime scene Search Patterns

• line

• spiral

• wheel

• quadrant/zone

• grid

line search pattern

One or two investigators start at the boundary of the crime scene and search in straight lines across to the other side of the crime scene

Grid Search Pattern 

Two or more investigators form a grid by searching in line patterns that overlap and are perpendicular to each other.

Spiral search pattern

One investigator searches in a spiral path from the center of the crime scene to the boundary (outward) or from the boundary of the crime scene to the center (inward).

Wheel/Ray Search Pattern

Several investigators search in straight lines from the center to the boundary (outward) or from the boundary to the center (inward).

Quadrant/Zone Search Pattern

The crime scene is divided into smaller sections (zones). One or more investigators are assigned to search each zone.

crime scene notes

Layout includes

• location of all evidence

• how evidence is packaged

• field testing of all evidence

• title block —> your name, title, location, date, time, case number

• All done in bleu or black ink and in a bound notebook

Crime scene sketch

• title block same as notes

• legend identifying object sketch

• compass showing north direction

• significant items/depicts layout

• possible paths of entry/exit

Photographs at a crime scene

4 minimum

1. close up → are taken last and show greater detail of individual objects or evidence (90 degree angle without evidence markers and scales)

2. overview →  of the entire scene and surrounding area, including points of exit and entry, are taken first (Include a “visual tag,” an object recorded in multiple overview photographs, to help visually piece the scene together)

3. close up with scale

4. medium range → Medium-range photographs show the layout of smaller significant areas of the crime scene

Lighting

Oblique lighting → uses a light source positioned at a low angle (shows us details with shadows on the surface of the evidence)

Types of Physical Evidence

almost anything can be physical evidence

drugs, fibers, fingerprints, weapons and amo, organs and body fluids, impressions, paint, petroleum products, tool marks, vehicle lights, etc.

Packaging Crime Scene Evidence (holders)

• pill bottle

• envelopes

• paper bag

• airtight tin container

• paper fold

A pill bottle collects and/or paper folds collect

small traces of evidence

ex: white powder

Anything paper (manilla envelope or paper bag)

Anything biological

ex: sweatpants with blood on them or swabs of blood

airtight metal container

anything to do with arson

Packaging biological evidance

if mold grows = dna degression = no result

any contamination or cross contamination = no result/manipulated result

Chain of custody

 list of all people who come into possession with of an item of evidence

This means that every person who handled or examined the evidence and where it is at all times must be accounted for. 

Known/standard reference sample

Physical evidence whose origin is known, such as blood or buccal (cheek) swab  from a suspect, that can be compared to crime-scene evidence.

• This is what you are comparing your evidence to

• Necessary in order to perform a comparison test

Substrate Control

 a sample collected near the evidence to insure the validity of the results

• Example: Silver car crashes into red car

• Evidence: silver transferred paint on red car

• Reference: silver paint from known suspect vehicle

• Substrate control: red paint from victim’s car, near the point of impact

Evidence sample

a specific physical, biological, or chemical specimen collected from crime scene victim or suspect that can be analyzed

Crime scene duties

1st responding officer (usually first person on scene police officer) will

• Acquiring medical assistance for injured victims

  • Medical personnel avoid disturbing evidence and approach the victim by an indirect route.

•  Detaining any potential suspects or witnesses

  • Statements are taken from victims, witnesses, and suspects

• Securing the crime scene to the greatest extent possible

  • All civilians and unauthorized personnel are excluded from the crime scene.

• Calling for any additional personnel needs, such as other officers and/or forensic investigators

  • The personnel required depends upon the nature of the crime scene.

The Lead Investigator will

• Securing the Crime Scene

  • The boundaries of the crime scene must be secured with crime scene tape, ropes, or cones

  • Include any area that evidence may be located.

  • Keep a log of anyone who enters/ leaves the scene

• A walk through → initial survey of the crime scene 

  • The perpetrator's point of entry and exit are located 

  • Indirect path is taken to the center of the crime scene 

  • Obvious items of evidence are located and documented 

  • The conditions of the scene are observed and recorded

    • Special attention is paid to items or conditions that suggest timing of the incident or do not appear they belong 

• Determine if it is a primary vs secondary crime scene 

  • Primary → where the original incident occurred 

  • Secondary → after initial incident

who ultimately decides the importance of the evidence

jury

Identification test

determine the physical or chemical identity of something (a known/standard doesn’t have to be tested with each sample)

Comparison Analysis

determine whether or not a known/standard and a piece of evidence have a common origin (both samples are subjected to the same tests)

class characteristics

evidence associated only with a group

individual characteristics

evidance that can be associated to one person

Primary crime scene

where the original incident occurred 

secondary crime scene

after initial incident