Crime Scene

Essential Question: Content Objective: Language Objective:

Crime scene 1 st on scene: 1 st priority: people safety 2 nd priority: secure the scene: keep people from altering evidence 3 rd priority: detain suspects/witnesses

Questions ASAP: as soon as possible Question 1 st on scene and witnesses about any transient evidence: Weather, odors, visibility, pts. Of entry/exit

Crime scene process #1: Safety #2: Secure the scene #3: Preliminary survey (boundaries, exits) Narative, photograph, sketch #4: Detailed search Narative, photograph, sketch #5: Record/collect data #6: Final survey – release crime scene

Preliminary Survey From outside the crime scene: do not know boundaries of crime scene body may have been dragged drugs may have been dropped while fleeing the scene

Preliminary Survey Narrative: detailed and legible Time line Measure scene and note locations Describe time of day, weather, lighting Written description of physical evidence Names of people involved

Preliminary Survey Photograph Before touch or move anything Take photos from different angles Have ruler for scale Photo from outside to inside in order Photograph each piece of evidence individually- and from far away

Preliminary Survey Sketch: key - scale - compass Original sketch is evidence in case Measurement: to scale - relative locations Scale: gives relationship of sketch to actual size Key: explains code used in sketch Compass: for orientation

Detailed survey From within the crime scene Photograph Sketch Narrative Collect evidence Initiate chain of custody

Chain of custody: a list of all persons who came into possession of an item of evidence

Custody Samples and data are considered to be in your custody when they are in your physical possession; they are in your view, after being in your physical possession they are in your physical possession and then locked up so that tampering cannot occur they are kept in a secured area, with access restricted to authorized personnel only.

Chain of custody Keep the number of people involved in collecting and handling samples and data to a minimum. Only allow people associated with the project to handle samples and data Always document the transfer of samples and data from one person to another on chain-of-custody forms Always accompany samples and data with their chain-of- custody forms.

Control Control: physical evidence whose origin is known (exemplar), such as blood or hair from a suspect that can be compared to crime-scene evidence Buccal swab: swab of inner portion of cheek; cheek cells are usually collected to determine the DNA profile of an individual

Collection of evidence Wet items: dry them, package them to prevent molding Biological items: freeze them. Fire arms: fixed inside wooden container Fumes (arson): kept in airtight container Collect most delicate items first (transient evidence)

Physical Evidence Types of physical evidence encountered at crime scenes. Difference between the identification and comparison of physical evidence. Physical evidence possessing individual and class characteristics. Value of class evidence to a criminal investigation

Identification: the process of determining a substance’s physical or chemical identity Comparison: the process of ascertaining whether two or more objects have a common origin Individual characteristics: properties of evidence that can be attributed to a unique source with an extremely high degree of certainty

Class characteristics: properties of evidence that can only be associated with a group and never with a single source Reconstruction: the method used to support a likely sequence of events by the observation and evaluation of physical evidence, as well as statements made by those involved with the incident

The Role of Forensic Science Provide scientific information to the legal community Done via reports and testimony A statement of the limitations on conclusions drawn from an experimental result is an essential element

Responsibility of the Analyst May conclude that an evidence object & a reference object show similar traits Must understand and communicate the limitations inherent in the conclusion limitations are a combined function of the nature of the traits the sensitivity and resolution of the detection methods the state of the evidence

Legal vs. Scientific Questions The law must establish that a crime has been committed by defining the corpus delecti (body of the crime) All elements that legally define any particular crime must be present to proceed The forensic scientist must translate the legal question into a scientific question

Thinking Forensically A cognitive framework for a forensic investigation

Fundamental Principles Transfer Locard Exchange Principle Identification placing objects in a class Individualization narrowing the class to one

The Locard Exchange Principle Every time an object comes into contact with another object, it either leaves a portion of itself or takes a portion of the other object with it Every contact leaves its trace

Transfer Physical movement of material from one place to another 1 mm fiber transferred from a sweater (its source) to a sweatshirt (its destination) during contact

Transfer No physical movement of material a pattern formed when an object makes an impression on some receptive substrate shoe stepping in mud (no detectable amount of leather left by shoe

Identification by Class Characteristics Classes of objects can be progressively narrowed by looking at successively more traits Results in continually fewer objects being classified as similar to each other If the traits being compared are not unique to the source item will possess traits that might be shared with a wide variety of sources

Once an object is identified by class, the object can be compared to a reference (known) item determine if it came from that source or some other

Individualization Individualization answers the forensic investigation questions Which one is it? (animate items) Whose is it? (inanimate items) Accomplished by examining traits that are unique to a source item any progeny can only have originated from that particular source item

Individualizing Traits Minutiae of friction ridges on fingers (fingerprints) nicks, cuts or gouges in a tire fine striae in the barrel of a firearm DNA markers

Individualizing Characteristics If two objects possess individualizing characteristics so that the analyst can conclude that no other items exhibit this array of traits association is absolute analyst concludes that the items share a common origin with each other latent print at crime scene and a reference set of prints made at the police station