Investigative Techniques in Criminal Investigations

Interviews are crucial for gathering information, but they're not always reliable. Police interview two main types of people: eyewitnesses (who saw the crime happen) and expert witnesses (specialists who provide technical advice). However, eyewitness testimony can be seriously flawed - one case shows how a rape victim wrongly identified Ronald Cotton from a photo lineup, leading to his wrongful imprisonment until DNA evidence later freed him.

Forensic techniques involve collecting physical evidence like blood, hair, fingerprints, and DNA from crime scenes. DNA analysis is particularly powerful because everyone has a unique DNA profile, making it brilliant for both proving guilt and innocence. It's highly reliable and can even identify victims when other methods fail.

However, DNA analysis isn't perfect. Suspects must already be on the National DNA Database to get a match, it's expensive, and cross-contamination can happen. Sometimes tiny amounts of DNA can falsely implicate innocent people - like taxi driver David Butler, whose skin condition caused his DNA to appear under a murder victim's fingernails when he was just giving her change.

Key Point: DNA evidence helped solve many cold cases and free wrongly convicted people, but it's not foolproof and requires careful handling to avoid contamination.

Surveillance techniques include CCTV cameras that constantly record public spaces and can deter crime. Covert surveillance involves secretly monitoring specific suspects through phone tapping and hidden cameras. This works brilliantly for serious crimes like terrorism because suspects don't know they're being watched, so they act naturally.

The downsides? CCTV cameras can't move to follow suspects, image quality often suffers, and footage gets deleted after 30-90 days. Covert surveillance raises privacy concerns and can lead to human error, plus there's the risk of entrapment where police essentially trick someone into committing a crime.

Offender profiling creates a psychological picture of criminals based on their behaviour and crime patterns. Geographical profiling analyses where crimes happen to predict where the offender lives. Typological profiling categorises crimes as either organised (planned, intelligent) or disorganised (impulsive, chaotic).

Profiling helped catch George Metesky, the "Mad Bomber" of New York in the 1940s, when he matched the profile almost perfectly. But it's not always accurate - criminals don't always fit neat categories, and profiles can be so vague they could apply to loads of people (called the Barnum effect).

Intelligence databases store vast amounts of information that police forces can quickly search and share. The Police National Database holds criminal activity records, while the Police National Computer includes DNA databases. International databases like INTERPOL help UK police access worldwide information on organised crime and exploitation.

These databases speed up investigations massively, but they're not without problems. Young people and ethnic minorities are over-represented, hackers could potentially breach security, and human error can corrupt the data.