CSI Strathclyde

This week's episode features our guest Martin Lupton, a former specialist Scenes of Crime officer, who spent several years as a uniformed police officer. Martin provides insight into the daily duties of those tasked with examining crime scenes for trace evidence of all kinds, based on Locard's Exchange Principle. This principle states that the perpetrator of a crime will bring something into the crime scene and leave with something from it. The following quote explains the principle well:

"Wherever he steps, whatever he touches, whatever he leaves, even unconsciously, will serve as a silent witness against him. Not only his fingerprints or his footprints, but his hair, the fibres from his clothes, the glass he breaks, the tool mark he leaves, the paint he scratches, the blood or semen he deposits or collects. All of these and more, bear mute witness against him. This is evidence that does not forget. It is not confused by the excitement of the moment. It is not absent because human witnesses are. It is factual evidence. Physical evidence cannot be wrong, it cannot perjure itself, it cannot be wholly absent. Only human failure to find it, study and understand it, can diminish its value." —Paul L. Kirk

Detectives working in rural offices often carry out their own scenes of crime examinations, which can be very satisfying and rewarding. There is nothing more pleasing than when a fingerprint lifted at a housebreaking, a fibre collected from a locus, or a sample of DNA is positively identified. It's a sign of a job well done and of the system working. This work is painstaking, requiring attention to detail, especially in horrible weather, in the middle of the night, or just before the end of a shift.

Like most high-reward endeavours, tenacity is required. There must be an acceptance that the result will be negative 99 times out of 100, but with the certain knowledge that if you persevere, do it right, and record it properly, the results will come, sometimes totally out of the blue.

Martin was kind enough to share his involvement in some of the worst murder cases, and we thank him for that. However, the truth is that officers everywhere are constantly searching for, photographing, recording, and submitting fibres, samples, and impressions in the pursuit of the slightest trace left behind by criminals who move among us otherwise unknown and undetected.