Published January 13, 2015
On TV, the fictional Las Vegas detectives on "CSI: Crime Scene Investigation" solve crimes each week by carrying clues like a single hair into the lab and emerging a short while later with a complete genetic profile of a suspect.
Reality is nothing like TV.
In the Baltimore Police Department's lab, DNA analysis is a painstaking, demanding process, counted in weeks if the investigators are lucky, in months if there are complications -- as there almost always are.
Once analysts in the serology section determine that a piece of evidence has biological traces -- bits of blood or tissue, for example – the samples are harvested and then move to a narrow back room of the section. There, DNA analysts cull the microscopic strands of genetic material from the enveloping cell.
It's a long process: Separating the DNA from other cellular components requires series of careful extractions. Sometimes, as in sexual assaults, male and female DNA is mixed together, and the analysts must separate those genetic puzzle pieces as well. The extraction can take a whole day, sometimes longer.
The serology lab, where analysts first look for human traces on crime evidence, is dominated by wide, flat surfaces to spread out evidence.
From there, the samples move across a carpeted office area for analysis in another
lab, separated from serology and extraction to avoid mix-ups or contaminants.
The separation of the labs is "good science," says Leon White, one of one of three analysts at the lab. Contamination "throws off the results."
The analysis lab is quiet and cool, full of computers, monitors, centrifuges and analyzers. Here, the DNA will be put through its paces.
First it will be copied, passed through hours of alternating heating and cooling cycles. Next, the sample will be analyzed by machines that determine individual genetic profiles, and compared against lab standards to make sure the results are accurate.
It takes at least a week to get usable data, on top of the time it takes for extraction, says White. Some runs have to be redone, lengthening the process even more.
Even then, the results -- thick sheaves of multicolored printouts -- must themselves be analyzed, another step in the slow road to building a DNA profile.
"The national average (for labs analyzing DNA) is four to five cases a month," says White. "That's about what we have."
In 2001, the lab's first year, the scientists there analyzed 45 DNA tests, including a 1991 case where the evidence eliminated four suspects, a rape case where the evidence matched a sample from a suspect, and another that exonerated one man already jailed on rape charges.
In 2002, the lab's output jumped to 71 samples, this time matching DNA profiles to suspects in 17 rapes,13 homicides and four assaults.
"The principles take a lot of time to put into practice," says White.
"It takes a lot to get meaningful information."