It's all in the detail

By Petro-Anne Vlok
12 March 2014

Evidence collected and analysed at the scene of a crime can make or break a case. Here’s how forensic teams go about their work.

Evidence collected and analysed at the scene of a crime can make or break a case. Here’s how forensic teams go about their work.

By Petro-Anne Vlok & Christiaan Boonzaier
Paralympic athlete Oscar Pistorius shot and killed his girlfriend, Reeva Steenkamp – that’s not in dispute. But there are two versions of how it happened: his defence team says he ran on his stumps into the bathroom and fired through the toilet door; the state claims he put on his prosthetic legs before he pulled the trigger. Only one person knows the truth: Oscar. There are no witnesses, and in cases such as this the law relies on painstakingly collected and meticulously analysed forensic evidence to determine exactly what happened. “It’s like putting a puzzle together,” ballistics expert Cobus Steyl says. Various forensic experts use their knowledge to create a picture.” When someone commits a crime, evidence is always left behind, leading forensic expert Dr David Klatzow says. “If you touch a window you leave fingerprints; if you walk on a carpet your shoes pick up traces of fibre. If you hit someone they’ll bruise.” We look more closely at how experts work a crime scene.

1. First member

  • When called out to a possible murder, the first police officer on the scene, called the first member, assesses if the victim is still alive. If so, the chief priority is to preserve life.
  • If the victim is dead, the officer secures the crime scene using SAPS-identifying tape. Officers are stationed to prevent unauthorised access.

2. Crime scene manager

  • The forensic department’s crime scene manager (CSM) relieves the first member. The CSM takes control of and responsibility for the scene and assigns crime scene technicians and an investigating officer (IO).
  • Next is the planning phase. The CSM, crime scene technicians and IO take a “first walk” through the crime scene, noting possible routes used by the victim or perpetrator as well as spotting what can be collected as evidence. They must take care not to disturb any evidence.
  • The CSM decides which experts and forensic resources are needed and the order in which the scene should be investigated.

3. Photographer

  • Before anyone may touch anything a photographer has to document the scene. Sometimes video documentation is also used or crime scene technicians make sketches.
  • 3D total station scanners are relatively new and effective documenting tools which take 3D images of the scene.

4. Crime scene technicians

  • They go through the scene with a fine-tooth comb. Because of the high crime rate in SA, crime scene technicians are often unavailable, in which case the IO collects evidence.
  • Technicians often use fluorescent light when searching for DNA samples. Blood, urine, semen and vomit show up in a bluish colour, even if the perpetrator tried to wash it off. UV light can help technicians see evidence hidden from the naked eye such as fingerprints, fibres and bruises on bodies.
  • Technicians are expected to keep meticulous records and note the date, time and place where evidence was collected.  Memory is fallible and wouldn’t hold up under cross-examination in court. Technicians have to label evidence as soon as they bag it.
  • After evidence has been collected on and around the victim, the body is taken to the morgue for further investigation by a forensic pathologist. Bags are placed over the hands and feet to preserve potential DNA evidence under the nails.
  • All collected evidence is preserved in evidence collection kits and sent to the forensic science laboratory for analysis.

Marking the scene

Coloured cones are placed throughout the crime scene to mark where evidence was collected. Each crime scene is different  but technicians can, for example, place yellow cones next to blood evidence. The cones are also used to map the crime scene. Where evidence is sent

What is collected as evidence?

Trace evidence: gunshot residue, paint residue, broken glass, unknown chemicals

Bodily fluids: blood, semen, saliva, vomit

Impressions: fingerprints, footprints, tool marks

Weapons and firearms: knives, guns, bullet holes, cartridge casings Documents and devices: diaries, suicide notes, computers, cellphones, memory sticks Hair and fibres


Adapted from YOU 14 March 2013 

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