Forensic Science in Crime Investigation: How They are Applied?

 

On Monday, May 13, 2024, I  briefly outlined the methods scientists used in forensic science to help the police in crime investigation in this link:

What is Forensic Science?

(https://scientificlogic.blogspot.com/search?q=forensic+science)

I shall now write a bit more on forensic science. We shall answer questions like what forensic scientists use to investigate a crime scene. We shall briefly describe the procedures, investigation methods they use, and how they conduct them to come to a conclusion from the crime scene, in the lab to the courtroom.

Let’s go together with me as a tour guide, shall we?

Forensic science is the application of scientific principles and techniques to solve crimes and help the legal system. Forensic scientists play a crucial role in criminal investigations, working closely with the police, law enforcement, prosecutors, and the courts. They collect and analyse evidence and provide expert testimony. 

Let us have a look at an overview of the procedures, investigation methods, and how forensic scientists work from the crime scene to the courtroom.

The first thing is the crime scene investigation. We need to secure the crime scene. Just like rescuers in a medical emergency, they have the First Responders.  The first priority at a crime scene is to ensure safety and provide medical assistance if needed. Once the area is secure, the scene is cordoned off to prevent contamination. Then we establish a perimeter.  This area is marked with tape, and entry is restricted to authorized personnel only. This prevents evidence from being disturbed or destroyed.

Next comes documentation where detailed photos are taken from multiple angles to capture the scene exactly as it was found. Then comes sketching where crime scene sketches provide a layout of the scene, showing the locations of key evidence. Detailed notes are then taken for documenting observations, the condition of the scene, and the position of evidence.

 Evidence is then collected using systematic search. By this I mean investigators conduct a systematic search of the scene, often using methods like grid, spiral, or zone searches to ensure no evidence is missed.

Next, comes evidence handling of items like blood samples, weapons, fibres, fingerprints, and other physical evidence that are carefully collected. Each piece of evidence is placed in separate, properly labelled containers to avoid cross-contamination. A record is kept of everyone who handles the evidence from the moment it’s collected to its presentation in court. This ensures the integrity of the evidence. We call this as chain of custody

The investigators then send the samples gathered for laboratory analysis. The types of analysis are fingerprint analysis. Fingerprints are lifted from surfaces using powders, chemicals, or alternative light sources. These are then compared to known prints. 

Then the DNA analysis where biological samples like blood, hair, or saliva are analysed for DNA. Techniques like Polymerase Chain Reaction (PCR) amplify the DNA, which is then compared to known samples. We also look at toxicology where blood and tissue samples are analysed for the presence of drugs, alcohol, or poisons. We also look for ballistics such as firearms and ammunition. They are examined to determine if a particular weapon was used in a crime. This involves matching bullets or shell casings to a specific firearm. Next, are trace evidence where small pieces of evidence, like hair, fibers, glass, and paint are analyzed to link a suspect to a crime scene.

In digital forensics, electronic devices are examined for evidence such as emails, texts, or files that could be relevant to the investigation.

Having said that, what are the scientific techniques we use? First, is microscopy where high-powered microscopes are used to examine trace evidence like hair, fibers, and particles. The chemists will then use spectroscopy with techniques like mass spectrometry or infrared spectroscopy used to identify chemical compounds in samples. Chemical analysis for various chemical tests is used to identify substances like drugs, explosives, or other materials found at the crime scene.

Next, we try to interpret and reconstruct the crime scene. We call this as reconstructing events.  Forensic scientists piece together the sequence of events based on the evidence collected. This might involve determining the position of the victim, the angle of entry of a bullet, or the sequence of blows in a violent encounter.

Bloodstain pattern analysis at a crime scene can reveal information about the position of the victim, the type of weapon used, and the movement of the victim or assailant during the crime.

Let me now talk a little about insects being used in the investigation. We call this as Forensic Entomology. Let me first give ourselves an introduction to Forensic Entomology. 

Forensic entomology is the study of insects and other arthropods in a legal context. It is primarily used to estimate the time since death (post-mortem interval, or PMI) by analyzing the types and developmental stages of insects found on a decomposing body.

 Insects are attracted to decomposing bodies and colonize them in predictable sequences, making them valuable in forensic investigations. 

How are insects used in forensic investigations? First, they are used for estimating time since Death (PMI). The primary application of forensic entomology is estimating the PMI. Different species of insects are attracted to a body at different stages of decomposition. By identifying the species and their developmental stage (e.g., eggs, larvae, pupae), forensic entomologists can estimate the time elapsed since death.

Insects are also used for locating a body.  Insects can also help locate a body by their presence in unusual numbers or species in certain locations. They can determine the movement of a body.  If insects typically found in one geographic area are discovered on a body found in a different location, it may indicate that the body was moved after death. In the area of toxicology, insects that feed on a decomposing body can sometimes be analyzed for the presence of drugs or toxins, especially if the body itself is too decomposed for traditional toxicology tests.

The process is called Collection of Insect Evidence.  Insects are collected from the body and the surrounding area. This includes both the insects on the body and those in the soil or other substrates around it. Next, is the identification and analysis. The collected insects are identified, and their life stages are analyzed. This helps in determining the species and estimating the PMI.

Environmental Factors such as temperature, humidity, and environmental conditions are taken into account, as they can affect insect development and thus the accuracy of the PMI estimate.

Of course, many people have heard about DNA collection and analysis, but they have no clue this is done. Let’s go into this very briefly in a non-technical way for everybody.

First, we need to do a DNA extraction and analysis. DNA extraction requires collection of samples. Biological samples like blood, saliva, hair, or tissue are collected from the crime scene or body. In some cases, bone or teeth may be used, especially in degraded or burnt remains.

The first thing is lysis of cells.  The first step in DNA extraction is breaking open the cells in the sample to release the DNA. This is done using a lysis buffer that breaks down the cell membranes. Next, we remove proteins and contaminants.  Proteins and other cellular materials are removed using a combination of chemicals and enzymes. This leaves behind a solution containing mostly DNA.

Next, we use purification procedures.  The DNA is purified from the solution, typically using techniques like ethanol precipitation or silica-based methods, to separate the DNA from other cellular components.

Having done that, we proceed to quantification where the amount of DNA is measured to ensure there is enough for analysis. Having done that, we proceed to DNA analysis using the following:

1.      Polymerase Chain Reaction (PCR): PCR is used to amplify the DNA, making millions of copies of specific regions of the DNA. This allows even small amounts of DNA to be analyzed.

2.      Electrophoresis: The amplified DNA is separated by size using a technique called gel electrophoresis. This creates a pattern that can be visualized and compared to known samples.

3.      Short Tandem Repeats (STR) Analysis: STR analysis focuses on specific regions of DNA that are highly variable between individuals. By analyzing the number of repeats at these regions, a unique DNA profile can be created.

4. Comparison: The DNA profile is compared to profiles from known individuals or entered into a DNA database (like CODIS) to see if there is a match.

Burnt Bodies:

What happens to the DNA in burnt bodies. Good question. Let’s look at the impact of heat on DNA. There may be thermal degradation. High temperatures can degrade DNA, breaking it down into smaller fragments or destroying it altogether. The extent of degradation depends on the duration and intensity of the heat exposure. Fortunately, there are also resilient samples.  Despite the destructive power of fire, some parts of the body, like teeth and bones, are more resilient and may still contain usable DNA. Bone marrow and the dense part of teeth (dentin) can sometimes protect DNA from complete destruction.

 DNA recovery from burnt bodies includes sampling from resilient tissues. In cases where the body is burnt beyond recognition, forensic scientists focus on collecting DNA from the most protected parts of the body, such as bones or teeth.

We can also use specialized techniques for recovery.  Forensic labs may use specialized techniques to recover and amplify even the smallest fragments of DNA from these samples, often requiring more advanced and sensitive methods than standard procedures. 

For example, we can use mitochondrial DNA analysis.  Mitochondrial DNA (mtDNA) is often used when nuclear DNA is too degraded. mtDNA is more abundant in cells and more resistant to damage, making it useful in degraded or ancient samples. However, it is less unique than nuclear DNA and is inherited maternally.

What are the challenges and limitations in severe degradation?  In cases of extreme heat exposure, DNA may be too degraded for any meaningful analysis. In such cases, identification may rely on other forensic methods like dental records, medical implants, or circumstantial evidence. Sometimes only a partial DNA profile can be obtained from a burnt body. While this can still be useful, it may not provide a conclusive identification without additional evidence.

Forensic entomology, DNA extraction, and analysis are all crucial tools in the forensic scientist's toolkit, helping to solve even the most challenging cases.

Next, is the timeline establishment.  Forensic scientists help establish a timeline of events, determining things like time of death through techniques such as body temperature measurement (algor mortis), rigor mortis, and livor mortis.

The forensic scientists after all the investigations, do the reporting and testimony

Forensic scientists write detailed reports on their findings, describing the methods used, the evidence analyzed, and the conclusions drawn. Reports are written in clear, non-technical language to be understandable to non-experts, including judges, and court prosecutors.

They then give their expert testimony in a courtroom presentation.  Forensic scientists may be called to testify in court as expert witnesses. They explain their findings, the methods used, and how they arrived at their conclusions.

During cross-examination, the defence may challenge the forensic scientist’s methods or conclusions. The forensic scientist must be able to defend their work and explain it clearly.

Forensic science is a meticulous and rigorous process that requires attention to detail, scientific expertise, and the ability to communicate complex findings in a clear and understandable manner. From securing the crime scene to providing expert testimony in court, forensic scientists are vital in ensuring that justice is served by providing objective, scientific evidence to support investigations.