Forensic Science: Warrantless Searches and Evidence Analysis
Warrantless Searches: Exceptions to the Fourth Amendment
The Fourth Amendment mandates a prior warrant for searches and seizures; however, several "special" circumstances allow warrantless searches:
Consent:
An officer may search and seize evidence or contraband if the person asked verbally agrees ("yes").
This consent does not automatically open every area; specific consent may be required for different spaces.
Only adults with a measure of control over the space can provide proper consent.
For instance, a roommate can consent to the search of their personal space and common areas but cannot authorize the search of another person's private property.
The consenting individual must possess ownership or similar rights over the space.
Searches during Legal Arrests:
Police officers have the right to search an arrested person and the immediate surrounding area to seize evidence.
This includes items found even if the person was later discovered to be incorrectly arrested, provided the arrest was made in "good faith."
The "immediate area" can encompass a person's car (though the trunk usually requires probable cause) or home/property.
A search of a home during an arrest must be limited to a "sweep" to ensure no threat to officers or the public exists; more extensive searches necessitate a warrant.
The guiding principle remains: "when in doubt, obtain a warrant."
Emergency Circumstances:
Warrantless searches are justified when there is insufficient time to obtain a formal search warrant and officials must act to protect individuals from hazard or prevent the immediate destruction of evidence.
Examples include officers entering a smoke-filled building to search for people or determine public threats, engaging in "hot pursuit" of a fleeing suspect, or responding to an emergency call.
Police can also intervene without a warrant if they believe evidence is being destroyed, such as drugs being flushed or alcohol being metabolized by the body.
Box 2.7: Body's Evidence
The U.S. Supreme Court ruled that a person can be compelled to take a blood alcohol test as part of a vehicular investigation without their consent or a search warrant.
The basis for this decision is that the body's normal biochemical processes destroy consumed alcohol.
Since blood alcohol constitutes evidence related to potential criminal DWI (driving while impaired) or DUI (driving under the influence) actions, the body's metabolism of alcohol is considered the destruction of evidence.
Therefore, requiring a blood sample for alcohol evidence without a warrant or consent is admissible under the Fourth Amendment.
Consequences of Unlawful Searches:
Evidence obtained unlawfully cannot be used as direct evidence in court proceedings.
Such evidence is, at best, legally useless and, at worst, damaging to a case.
It is crucial for investigators to conduct searches lawfully to ensure the admissibility of evidence in court.
Plain View:
This doctrine applies to items visible from a legal vantage point, such as objects seen through a window or openly from a public place.
Officers conducting a warrant-based search may also seize items not listed in the original warrant if they are in "plain view."
There are subtleties to this doctrine; for example, in California v. Ciraolo (), the Supreme Court allowed police to fly over and observe a person's home from an altitude of without a warrant to search for contraband, even though the fenced-in yard was not visible from ground level.
Airport, Border, and Sea Searches:
Warrantless searches of individuals and their luggage are legal at airports, transportation centers, and international borders to protect public safety.
This includes luggage scanning, personal body scans, and physical searches.
If agents have reasonable suspicion, a more thorough, "non-routine" search may be justified, often without warrants, potentially including strip and cavity searches.
The main decks of boats can be searched without a warrant, but interior compartments typically require probable cause and warrants.
"Stop and Frisk":
An officer may detain and perform a "pat down search" or "frisk" if they suspect a person is engaged in, or about to engage in, criminal activity, possesses a weapon, or poses an immediate threat to the public.
If the officer feels something like a weapon on the suspect during the pat down, they can reach in and seize it without a warrant.
Inventory Searches:
Officials are permitted to search anything seized as part of an investigation or arrest (e.g., automobile, airplane, boat) while creating an inventory of its contents.
The inventory serves to protect the owner's property and shield the police from false claims of missing or damaged items.
If illegal materials are found during this process, they can be collected as evidence.
National Security:
Under the USA Patriot Act and similar international laws, email messages, medical and financial records, and other personal information may be searched without a warrant, though other types of surveillance may still require one.
These provisions are enacted by Congress and have been allowed by the Supreme Court, with the possibility of future modifications.
National security searches are subject to varying rules regarding their application, but investigators are often granted wide latitude in defining what constitutes a national security-related search.
Administrative Searches:
Certain agencies, such as fire, electric, gas, and safety inspectors, can conduct warrantless searches.
However, these searches typically cannot directly provide evidence for criminal cases.
They can, nonetheless, alert authorities who can then seek a normal search warrant to search and seize the previously observed items.
Crime Scene Investigations: Introduction to Evidence
Paul L. Kirk's Axiom: In the words of forensic scientist Paul L. Kirk (–): "Evidence that does not forget…it is factual evidence, physical evidence cannot be wrong, it cannot perjure itself…only its interpretation can err."
Learning Goals and Objectives (Chapter Overview):
Discuss proper evidence collection, recording, and storage.
Describe the "chain of custody."
Define physical evidence.
Explain when evidence is admissible or inadmissible in court.
Identify class and individual characteristics of evidence.
Understand types of comparison analyses.
Explain probative and prejudicial evidence.
Identify key features of the Fourth Amendment related to evidence collection.
Determine search warrant requirements.
Recognize legal allowances for warrantless searches.
Discuss outcomes of key cases regarding evidence collection.
Describe circumstances leading to inadmissible evidence.
Determine proper crime scene processing steps.
Identify possible evidence team members and their roles.
Introduction: What is Evidence?
Forensic evidence aims to connect two entities, such as a suspect to a crime scene, a weapon to a wound, a computer message to a criminal act, or a poison to a cause of death.
Material evidence, consisting of physical items, most commonly serves this crucial linking role.
Ideally, the link between an item of evidence and its source should be unambiguous, uniquely connecting one person to one crime scene.
Locard's Principle: States that when two objects come into contact, a transfer of material occurs.
The challenge lies in discovering, collecting, and analyzing this transferred material to establish the connection.
Unlike fictional portrayals, evidence at a crime scene is not labeled and is often hidden among irrelevant "environmental" items, making its discovery akin to finding a "needle in a haystack."
The ability to recognize the potential relevance of an item is a key ingredient in investigations.
Importance of Crime Scene Evidence:
Crime scene evidence forms the critical core of forensic investigations.
Accurate observations and measurements are fundamental to data analysis.
To be useful forensic evidence, it must be legally collected.
The identification, collection, handling, and storage of evidence from a crime scene are vital for its use in investigations and admissibility in courtrooms.
Fiction vs. Real World of Forensic Science:
In television and movies, investigators often quickly locate a crucial piece of evidence, solving the case instantaneously.
In reality, crime scene investigations require extensive hard work, skill, experience, and insight to locate and link forensic evidence into a logical chain of events.
It demands a finely-honed ability to observe and perceive important information amidst ambient "background noise."
Proper crime scene processing often involves a diverse array of specialized experts, including anthropologists, medical examiners, entomologists, fingerprint experts, photographers, firearm analysts, and others, each contributing unique skills and insights.
Value and Admissibility of Forensic Evidence:
The inherent value of forensic evidence is determined by its ability to inform the "trier of fact" (the court).
Evidence that fails to serve this informing role is legally useless and typically inadmissible.
Evidence must be more probative than prejudicial.
Box 2.1: Probative vs. Prejudicial Evidence
Relevant Evidence (from FRE ): Evidence capable of making the existence of any fact important to the case more or less probable.
Probative: Evidence that possesses the ability to prove or demonstrate something relevant to the case.
Prejudicial: Evidence pertaining to a previously established matter (e.g., a prior conviction) or that creates a preconceived bias in a matter being decided.
While all evidence against a person is somewhat prejudicial, it must not be unfairly prejudicial.
Types of Evidence
Evidence encompasses anything introduced as part of a trial, taking various forms.
Physical Evidence: Generally refers to a material object, such as a weapon, fingerprint, or clothing item, that can be observed and measured.
This is part of a broader spectrum of forensic evidence, which includes: chemical, biological, cyber, linguistic, and behavioral evidence.
Evidence typically provides two main types of information: identification or comparison analysis.
Identification and Comparison Analysis
Identification Analysis:
Focuses on describing, in extensive detail, the components or composition of an unknown sample.
The goal is to identify relevant features of evidence with maximum specificity and certainty, leading to an unambiguous identification of the material and its composition (e.g., cocaine, cotton fiber, lead pipe).
For example, determining the chemical composition of an unknown sample is often provided by forensic laboratory analysis.
Evidence samples can originate from crime scenes, scraped from weapons, wiped from a suspect's hands, or collected during an autopsy.
The analysis typically aims to determine the specific identity of a substance, such as heroin, glucose, or strychnine.
Laboratories must carefully consider the type of information required and the most effective methods to obtain useful data.
Chapter , for instance, will discuss how light can be used to unambiguously identify the chemical composition of unknown materials (e.g., distinguishing an illicit drug from a harmless household compound).
Often, multiple analytical methods are employed to verify the identification; greater confidence is achieved when divergent methods yield similar results.
Comparison Analysis (vs. Identification):
Attempts to associate a standard reference sample (termed an exemplar) from a known origin with a sample of unknown origin (typically from a crime scene or a suspect).
The specific objective is to determine if both samples (the exemplar and the unknown) share a common origin.
Examples: determining if a blood sample from a crime scene and a suspect's blood sample share a common source, or if a fingerprint found on a weapon matches prints taken directly from a suspect.
These analyses are highly prevalent in forensic investigations and are frequently used for evidence such as fingerprints, DNA, bullets (Figure ), bones, patterns, and ecological samples.
The ability to establish this connection helps place a suspect at a particular location and either refute or support a hypothesis regarding a chain of events.
Types of Comparison Analysis:
One-to-Many Matching:
Involves matching key features found in an unknown sample with potential candidates from a very large pool—often millions—of known possibilities.
A simple illustration is comparing one block against many in a set to find a match (Figure ).
Forensic applications include matching an unknown fingerprint from a crime scene against massive databanks, identifying unknown human remains through DNA comparison to a large database, or rapidly comparing the spectrum of an unknown chemical against a databank of millions of known compounds (Figure ).
This approach is highly suitable for computer-based searching processes using stored records.
Computer search strategies compare features of the unknown to stored records of known origin in databases to find the best matches.
Frequently employed databases include fingerprints, DNA profiles, eye iris patterns, handgun firing pin patterns, automotive paint profiles, and various biometric information.
One-to-One Matching (Verification or Authentication):
Focuses on comparing a set of observed features in an unknown sample with either a single reference sample or a very small number of "standard" samples.