Explosives and Ballistics Evidence

Forensic analysis of explosives and firearms plays a critical role in solving crimes involving these dangerous materials. These types of evidence in forensic science provide valuable insights into the nature of the crime and help identify potential suspects.

Explosives analysis involves determining the chemical composition of explosive substances to identify their type and origin. Trace evidence of explosives can be found on a suspect's clothing, skin, hair, or other objects and matched to explosives from a crime scene. Additionally, materials used to construct explosive devices are compared to evidence found in a suspect's possession to confirm a match.

Vocabulary: Gunshot Residue $GSR$ - Particles expelled when a firearm is discharged, which can be detected on a person's hands, face, or clothing.

Ballistics evidence examination focuses on the characteristics of ammunition, firearms, and residue. Key aspects of ballistics analysis include:

1. Chemical tests to reveal gunshot residue $GSR$ on hands, face, or clothing
2. Examination of rifling marks on fired bullets to match them to specific weapons
3. Use of the Integrated Ballistics Identification System $IBIS$ database to compare markings from ballistic evidence

Highlight: The analysis of gunshot residue in forensic investigation can indicate how close a person was to a fired gun, providing crucial information about their involvement in a shooting incident.

Dust and dirt evidence can also reveal valuable information about a person's movements or connections to a crime scene. Investigators examine samples for chemical composition, pollen, plant material, and organic matter to establish links to specific locations.

Fingerprints and Fracture Matches

Fingerprint analysis and fracture matching are crucial techniques in forensic science, providing unique identifiers that can link suspects to crime scenes or piece together fragmented evidence.

Fingerprint Analysis: Investigators identify unique ridge characteristics in fingerprints to identify suspects or victims. The Automated Fingerprint Identification System $AFIS$ is a database used by law enforcement at local, state, and national levels to search for matches to fingerprints found at crime scenes.

Definition: AFIS $Automated Fingerprint Identification System$ - A computerized system used to store, search, and retrieve fingerprint data for law enforcement purposes.

Fracture Matches: When an object is broken, torn, or cut, two unique edges are formed, called fracture lines. These edges can be compared visually or microscopically to determine if they fit together, indicating they were once part of the same object.

Example: Investigators might compare edges on pieces of tape, glass fragments, paint chips, or car parts from an accident to find possible matches.

Impression Evidence: Shoeprints and tire tracks are forms of impression evidence that can provide valuable leads in a case. This evidence can be:

• Photographed
• Lifted with tape
• Cast with plaster

Investigators identify patterns to determine brands and other physical features. Wear patterns and unique characteristics like scratches or cuts can be used to match evidence to specific items.

Highlight: The analysis of impression evidence can provide crucial information about the type of shoes or vehicles involved in a crime, narrowing down the pool of potential suspects.

Tool Marks, Questioned Documents, and Biological Evidence

Forensic science utilizes various types of evidence in forensic science to solve crimes, including tool marks, questioned documents, and biological samples. These pieces of evidence provide crucial information that can link suspects to crime scenes and help investigators reconstruct events.

Tool Marks: As tools are used, tiny nicks and chips form on their edges, creating unique patterns that can be used to identify matches between evidence and suspects. Tools may also pick up traces of blood or other substances that can be tested, or have fingerprints that can be lifted.

Questioned Documents: Document examiners analyze items such as ransom notes or other suspicious documents to find clues linking them to a crime scene or specific suspect. They examine:

• Type of paper used
• Printing method
• Handwriting style
• Type of ink
• Unique features like watermarks or indentations

Example: Indentations made as someone wrote on a page in a notebook can provide useful clues about the document's origin or content.

Serology and DNA Evidence: Biological evidence such as blood, semen, saliva, sweat, and urine can provide valuable information about a crime, its victim, or suspects.

Vocabulary: CODIS $Combined DNA Index System$ - A database maintained by the FBI used to find matches to unknown DNA samples from crime scenes.

Key points about biological evidence collection and analysis:

1. Chemicals and ultraviolet light are used at crime scenes to locate body fluid evidence.
2. Potential evidence areas are swabbed, bagged, and collected in airtight vials to prevent cross-contamination.
3. DNA can be extracted from various tissues, including hair, fingernails, bones, and teeth.
4. DNA profiles created from evidence can be compared to profiles from suspects or victims.

Highlight: The use of DNA evidence and databases like CODIS has revolutionized forensic science, allowing for the identification of suspects and the resolution of cold cases.

Skeletal Remains and Forensic Anthropology

Forensic anthropology is a specialized field within forensic science that focuses on the analysis of skeletal remains. This discipline plays a crucial role in identifying victims, determining cause of death, and providing valuable information in criminal investigations.

Forensic anthropologists analyze skeletal remains to determine four key characteristics:

1. Age at death
2. Sex
3. Ancestry
4. Stature $height$

Definition: Forensic Anthropology - The application of physical anthropology techniques to legal cases, particularly in the identification and analysis of human skeletal remains.

These experts use various methods to extract information from bones, including:

• Morphological analysis: Examining the shape and structure of bones
• Metric analysis: Taking precise measurements of bones
• Microscopic examination: Looking at bone tissue under high magnification
• Chemical analysis: Studying the composition of bones for additional clues

Highlight: Forensic anthropology is particularly valuable in cases involving decomposed or skeletonized remains, where traditional identification methods may not be applicable.

The information gathered by forensic anthropologists can help:

• Identify unknown victims
• Estimate time since death
• Determine circumstances surrounding death
• Provide evidence of trauma or pathological conditions

Example: In a case involving unidentified skeletal remains, a forensic anthropologist might determine that the victim was a male in his mid-30s, approximately 5'10" tall, and of European ancestry, narrowing down the pool of potential missing persons.

By combining their expertise with other forensic disciplines, such as DNA analysis and forensic odontology, forensic anthropologists contribute significantly to the resolution of complex criminal cases and the identification of missing persons.

Paint and Glass Evidence in Forensic Science

Forensic scientists analyze paint and glass evidence to connect suspects, victims, and crime scenes. These types of physical evidence provide valuable information in various criminal investigations.

Paint evidence analysis involves both physical and chemical examinations. Investigators can determine the class of paint, such as automobile paint or nail polish, and compare it with database samples to identify specific brands or types of vehicles. Paint chips can also reveal individual characteristics, allowing for precise matching between crime scene evidence and potential sources.

Example: A paint chip found at a hit-and-run scene could be matched to a suspect's vehicle by comparing color, number of layers, and chemical composition.

Glass evidence is commonly found in crimes involving breaking and entering, hit-and-run incidents, vandalism, or murder. Forensic analysis of glass particles includes examining:

• Color
• Surface characteristics
• Tint
• Thickness
• Density
• Chemical composition
• Refractive index $RI$

Highlight: The results of glass analysis provide crucial clues for investigators to establish connections between suspects, victims, and crime scenes.