Exclusive: How to catch a criminal through DNA
Cape Town - The gleaming floors of the Police Forensics Laboratory reflect the light from the energy-saving intelligent fluorescent lighting above.
Colonel Thembela Lamani, head of the Biology unit, leads the Cape Argus team through the silent halls of strictly secured offices and laboratories in the Plattekloof facility.
Inside the glass-walled labs, scrubbed technicians busy themselves with some of the most sensitive work the Cape Town facility handles.
Cross contamination is a constant risk and needs to be mitigated as stringently as possible.
The controls are so stringent that the Cape Argus team needs to undergo DNA profiling just to enter the unit.
Two technicians clinically swab epithelial tissue from the team, using equipment out of hermetically sealed buccal kits - specifically designed to obtain the purest sample of DNA from the inside cheek wall of the mouth. By the time the swabs are clicked into place against the contact pad, chemicals begin to break down the proteins in the tissue and isolate the DNA strands. By the time they are inserted into one of three reference index lanes housed in the facility’s basement, the DNA is ready for gene mapping in accordance with the DNA Act of 2013.
The team needs to be entered into the database in the event of any possible cross-contamination - a sneeze, an accidental touch, a cough, or a mistimed clearing of the throat - affecting the sampling process inside the labs, so that in the event of a sample picking up a particular gene map, the Cape Argus team can be ruled off the list of suspects, as they would have been recorded as visitors to the lab. Evidence of which can be proven in court.
Brigadier Deon Meintjes, who runs the facility, says: “No one can tamper with the list. We take your DNA and map it, but we can’t add you to an offender database. This is just for security.”
Lamani leads us into the lab.
Clothing samples hang in glass-doored drying cupboards. Sprawling testing tables lie central in the evidence extraction lab.
On these tables, clothing suspected of containing bodily fluids - blood or semen - is subjected to presumptive tests.
Reagents are used to determine whether stains presumed to be bodily fluids are indeed blood or semen. From there, a small piece of material - a 50mm by 50mm swatch - is cut up and put into trays of vials to be forwarded to the isolation lab.
Also read: Exclusive: Inside the SAPS’ Forensics Lab
The evidence recovery room is strictly controlled, as cross contamination can easily occur.
Once the sliver of evidence is extracted in the isolation lab, it can then be sent for quantification and amplification.
“But if at this stage we can’t extract DNA, we close the investigation. We can’t prove it, we can’t map it,” Lamani says.
To extract DNA from a single sperm cell, Lamani says, takes around six hours.
If it is confirmed by the isolation lab, the DNA can then be quantified and amplified. Prior to this step, the DNA degrades over time. But once quantified, amplified and stored, it’s evidence that can last for years.
The DNA material then goes to the electrophoresis lab. The equipment used in this lab cost about R2 million each. There are six of these machines. The apparatus uses capillary rays to take “pictures” of the DNA in order to visualise it. By visualising the DNA, the Writing Reporting Officer is able to compare the DNA to the suspect, and is able to present a report to the courts.
In the bowels of the facility, a unit dedicated to loading DNA into dedicated reference index lanes directly from buccal samples runs a tight ship.
The Cape Argus team is made to put plastic shoe slips over their shoes before entering the vaulted space. In line with the DNA Act, the genetic maps are loaded onto a database in a slick, automated process.In another wing, Colonel Noko Mabala heads yet another analysis unit which focuses on images, audio and video recordings, and administers polygraph tests.
“Sometimes they confess before the polygraph,” he chuckles.
In the image enhancement lab, a warrant officer explains that his job entails ensuring video evidence from CCTV cameras hasn’t been tampered with, by checking for changes in lighting, syncing, and even goes as far as matching the meta data with the time code imprinted in the image.
In the basement, the interrogation room can be accessed from the basement, fully secure “for people who think they can do a runner when they come for polygraph” Mabala says. The room is comfortable and has its own holding cell for suspected offenders.
“You must have slept at least five hours before we polygraph you. If not, some of your responses are still asleep. You can’t be on medication, because then it’s the medication giving responses. We interview you for hours before we even hook you up to the polygraph. We want you to fully understand what’s going on and what the consequences and definitions of your actions were and are.
“There are sensors we put around you, there are sensors in the chair, there are even sensors in the floor taking readings. We’re thorough and we’re accurate. We won’t administer a polygraph if you’re not ready to take it,” Mabala says.
“Trust me, private companies aren’t nearly as thorough as we are. We are very thorough. We do get confessions.”