How to Solve a Crime

1. Forensic science combines meticulous analysis with creative problem-solving

Because forensics can involve anything and everything encountered in everyday life, attempting to cover every aspect of it would be a very tall order.

Breadth of forensic science. Forensic science encompasses a vast array of disciplines, from biology and chemistry to physics and psychology. It involves analyzing evidence from crime scenes, reconstructing events, and linking suspects to crimes through trace evidence. Key areas include:

• DNA analysis
• Fingerprint examination
• Ballistics
• Toxicology
• Digital forensics
• Entomology
• Anthropology

Creative thinking. Forensic scientists must think creatively to solve complex puzzles. This often involves developing new techniques, adapting existing methods to unique situations, and considering unconventional approaches to evidence analysis. Success in forensics requires not just technical expertise, but also imagination and the ability to see connections that others might miss.

2. DNA profiling revolutionized criminal investigations but isn't infallible

With DNA grouping, it was usually only possible to say, at best, that there was a one in a few thousand chance of a particular blood sample having come from someone other than the suspect or victim. With DNA profiling, that chance will be nearer one in a billion – which makes blood a more powerful form of evidence than ever.

Power of DNA evidence. DNA profiling has transformed forensic science since its introduction in the 1980s. It can provide extremely strong evidence linking suspects to crime scenes or victims, with match probabilities often in the billions to one. DNA evidence has helped solve countless cold cases and exonerate wrongly convicted individuals.

Limitations and challenges. Despite its power, DNA evidence isn't perfect:

• Contamination can lead to false results
• Partial profiles may be less conclusive
• Mixed samples can be difficult to interpret
• DNA transfer can occur innocently, leading to misleading conclusions

Forensic scientists must carefully consider the context of DNA evidence and corroborate it with other forms of evidence whenever possible.

3. Trace evidence like fibers and glass can provide crucial links in cases

Just like every other type of forensic evidence, rope is never just 'any old rope'. It has its own distinguishing features relating to what it's made from and how these constituents have been woven or twisted together.

Types of trace evidence. Trace evidence encompasses microscopic materials transferred between people, objects, and locations during a crime. Common types include:

• Textile fibers
• Glass fragments
• Paint chips
• Soil particles
• Hair

Analysis and interpretation. Forensic scientists use sophisticated techniques to analyze trace evidence, including microscopy, spectroscopy, and chemical analysis. The value of trace evidence lies not just in individual matches, but in the combination of multiple types of evidence creating a stronger overall case.

Challenges. Trace evidence can be easily contaminated or lost, requiring careful collection and handling procedures. Interpreting the significance of trace evidence also requires consideration of alternative innocent explanations for its presence.

4. Digital forensics and CCTV analysis are increasingly important tools

The whole digital revolution has happened since the start of my career as a forensic scientist in the 1970s. Today, digital forensics is one of the three most requested forms of forensic testing, along with DNA and fingerprints.

Growing importance. As technology permeates every aspect of life, digital evidence has become crucial in many investigations. Key areas include:

• Computer forensics
• Mobile device analysis
• Network forensics
• CCTV footage examination

Types of digital evidence. Digital forensics can reveal a wealth of information:

• Communications (emails, messages, call logs)
• Location data
• Internet search history
• Deleted files
• Financial transactions

Challenges. Digital forensics faces unique challenges, including rapidly evolving technology, encryption, and the sheer volume of data to analyze. Forensic experts must continually update their skills and tools to keep pace with technological advancements.

5. Cold case investigations require innovative approaches and persistence

There are many additional challenges with cold-case investigations. These include the fact that the crime scene in its original state is long gone, so you have to rely on plans and photographs, police briefings, witness descriptions, and initial forensic and other expert reports and case notes to recreate it in the mind's eye.

Challenges of cold cases. Cold case investigations face numerous obstacles:

• Degraded physical evidence
• Fading memories of witnesses
• Lost or incomplete case files
• Changes in forensic techniques over time

Innovative approaches. Solving cold cases often requires:

• Re-examining evidence with new technologies
• Fresh perspectives on old theories
• Creative use of genealogical databases
• Leveraging media attention to generate new leads

Importance of persistence. Many cold cases are solved through sheer determination and refusing to give up, even after years or decades. Advances in forensic techniques, particularly DNA analysis, have led to breakthroughs in cases long thought unsolvable.

6. Forensic toxicology helps solve poisonings and unexplained deaths

As the sixteenth-century German-Swiss physician known as Paracelsus famously remarked: 'All substances are poisonous, the only thing that distinguishes them is the dose.'

Role of toxicology. Forensic toxicologists analyze biological samples and crime scene evidence to detect the presence of drugs, poisons, and other toxic substances. This is crucial in:

• Suspected poisonings
• Drug-related deaths
• DUI cases
• Workplace drug testing

Analytical techniques. Toxicologists use a range of sophisticated methods:

• Gas chromatography-mass spectrometry (GC-MS)
• Liquid chromatography-mass spectrometry (LC-MS)
• Immunoassays
• Spectrophotometry

Challenges. Toxicology faces challenges such as new designer drugs, complex drug interactions, and postmortem changes affecting substance concentrations. Interpretation of results requires understanding of pharmacology, metabolism, and potential innocent explanations for the presence of substances.

7. Quality control and preventing contamination are critical in forensics

Because such errors can – and do – occur, it is essential for any provider of forensic services to have a rigorous system of quality management in place. Robust quality systems are absolutely key to every aspect of forensic science, so that the scientists themselves know they are doing things correctly, and so that other people can also have confidence in their results.

Importance of quality control. Rigorous quality management is essential in forensic science to ensure reliability and prevent errors that could lead to miscarriages of justice. Key aspects include:

• Standardized procedures
• Regular proficiency testing
• Peer review of results
• Proper documentation and chain of custody

Contamination prevention. Contamination can invalidate evidence or lead to false conclusions. Measures to prevent it include:

• Clean room environments
• Proper protective equipment
• Separation of evidence from different cases
• Regular cleaning and decontamination of equipment

Accreditation and oversight. Many forensic laboratories now seek accreditation from external bodies to demonstrate adherence to quality standards. This helps maintain public trust in forensic evidence presented in court.

8. Plant material and pollen can provide unexpected forensic evidence

Forensic biologists examine all types of plant material – pollen, seeds, fruits, leaves, wood, bark and roots – to investigate both criminal and civil cases.

Types of plant evidence. Plant material can provide valuable forensic clues:

• Pollen grains linking suspects to crime scenes
• Wood fragments from weapons or tools
• Plant residues on clothing or vehicles
• Toxic plants in poisoning cases

Analysis techniques. Forensic botanists use various methods:

• Microscopy
• DNA analysis
• Chemical profiling
• Comparison with reference collections

Applications. Plant evidence can help in:

• Determining time and location of crimes
• Linking suspects to scenes
• Identifying the origin of drugs or other contraband
• Providing circumstantial evidence of activities

9. Presenting scientific evidence effectively in court is a crucial skill

Sometimes, opposing counsel might try to discredit any evidence that doesn't suit their case by accusing the witness of incompetence or bias. Occasionally their cross-examination can be quite aggressive. But however insulting and wide of the mark their accusations might be, it is important to remain calm.

Challenges of testimony. Forensic scientists must effectively communicate complex scientific concepts to judges and juries who may have little scientific background. This requires:

• Clear, jargon-free explanations
• Use of analogies and visual aids
• Honest acknowledgment of limitations and uncertainties

Maintaining objectivity. Forensic experts must remain impartial and resist pressure to overstate conclusions or take sides. Their role is to present the scientific evidence accurately, regardless of its implications for the case.

Preparation and composure. Effective court testimony requires thorough preparation and the ability to remain calm under aggressive cross-examination. Scientists must be able to defend their methods and conclusions while admitting any limitations or uncertainties in their work.

Last updated: May 10, 2025