Familial DNA: Hanging From The Family Tree

Lonnie Franklin, Jr., aka the Grim Sleeper, was finally caught and charged with his crimes. Franklin, a serial killer who murdered ten women in two separate killing sprees beginning as early as 1985, wasn’t caught in the normal Sherlock-Holmesish manner. No, detectives didn’t use line-ups, interrogations, or lie detectors. No magnifying glasses and fingerprint comparison. In the beginning they’d didn’t even resort to conventional DNA testing or CODIS to help locate their suspect. Instead, they used a controversial method of DNA testing called Familial DNA.

Familial DNA testing differs from the traditional DNA testing where near 100% slam-dunk-accurate results are achieved by comparing DNA found at the crime to the suspect’s DNA. This manner of DNA testing compares close-but-not-exact matches of evidence gathered at the crime scene to the state’s DNA database (only two states, California and Colorado, allow the use of familial DNA for criminal cases). In California, a total of 1.3 felons have DNA samples registered in the system.

This still much-debated manner of DNA testing focused (in Franklin’s case) on 15 areas of DNA on 13 chromosomes, which included the 13 regions used by the FBI’s CODIS system, and two additional regions required by the state of California. What scientists hoped to find were patterns of base pairs that repeated themselves over and over again (short tandem repeats). If found, it’s highly possible and maybe even probable (note that I said possible and maybe probable) that those similar repeating patterns could point to people who are related. But, the shared pattern must be a rare variation of the repeat rather than a common one in order for the results to point to a family member.

Scientists use software to generate a list of very close relatives (parents, full siblings, and children) from a DNA database. They look for these very close matches because the statistics simply aren’t sound enough to identify relatives any further down the family tree. If the matches are male, scientists are able to determine if the connection is between father and son, or full brothers. They do so by examining the Y chromosome.

In the Franklin case, a second possible match turned up—Christopher Franklin, the son of Lonnie Franklin, Jr. Christopher Franklin was in the database because he’d been arrested on a felony weapons charge. However, other evidence ruled out the possibility that he was the killer. Therefore, officers focused their attention on Lonnie Franklin, Jr. They followed the elder Franklin and finally obtained a sample of his actual DNA by recovering a partially eaten piece of pizza. Franklin’s DNA matched the DNA (using traditional DNA testing) found at one of the crime scenes, and police arrested him at his home last week on July 7.

Familial DNA testing seems to working quite well. However, there are drawbacks. Scientists say that out of a million or so people, hundreds of other individuals could have a close enough match on CODIS markers to indicate that they are indeed a relative, even if they’re not. Reasonable doubt? Certainly. Slam dunk? Certainly not. Will Lonnie Franklin, Jr. be convicted based on a familial DNA search? Maybe so, maybe no. Let’s hope so, but the doubt has already been planted. After all, the search also indicated his son. Who else could be implicated if the search was conducted over a larger area? Suppose the defense opens up the can of worms that the killer could have come from another state? Did authorities test people from those areas? Nope. But, authorities have successfully convicted criminals based on familial DNA searches. For example, it led to a guilty plea in a car theft case in Colorado in 2009. Still, notice the conviction was based on a plea agreement, not on evidence alone.

I’m anxious to see how this one turns out.

L.A. Now photo