I've had a long post that I've been meaning to write regarding the DNA in this case. I wanted to address some of the thoughts often posted here such as, because they haven't announced a hit in CODIS or a familial genealogy hit yet, LE doesn't have DNA to work with. Or that this must mean BG has never offended before (and the host of crazy theories that surround this thought).
First of all, I have not made a secret of my opinion that this was a sexually-oriented crime and so everything I write in this post will have that motive as the background. (This not to say that all sexually oriented offenses will yield a DNA sample, but I believe this one did.) I think that the statistics surrounding abductions/murders of females in this age group and under these circumstances bear this out but if you are of the opinion that they were killed because they knew a secret or because they saw someone cooking meth, then you may not want to read on.
I think the key to understanding the DNA in this case can be found in the following article:
An Epidemic of Disbelief
This article is about serial rape and how and why sexual offenders so often get away with it.
I'll paraphrase some points that relate to the Delphi Murders, in my opinion. First of all, there is an epidemic of untested rape kits in the US. This article cites a number of perhaps 200,000 untested kits. Another source says that there are about 4,989 untested kits in Indiana alone. I would be willing to bet that the DNA match to the Delphi case is in one or more of those kits and here's why.
Serial rapists (who sometimes graduate to murder) are more common than previously believed. In 49 out of 50 rape cases the alleged assailant is never prosecuted (for various reasons). According to the article, this means that out of all the violent crimes, rape is the easiest to get away with.
In the article, you can read about how some of these offenders "prepare" for their crimes...by shaving their bodies, bringing condoms, or planning to wash the victims with water. These criminals can be very wise to DNA and prepare accordingly.
In Cleveland, a serial rapist graduated to serial murder (Anthony Sowell). After LE discovered his murders and linked them to the serial rapes, they discovered that none of his previous attacks where women survived had ever been investigated nor the rape kitse tested. Perhaps BG, too, has a trail of untested and unlinked victims that contain evidence as to his identity.
Probably most enlightening thing in the linked article is the info that HOW rapists offend and WHO they select as victims is very different than what our conventional wisdom tells us. Everyone assumes, and I've seen it on this forum many times, that rapists/murderers have a "type" of victim as well as a style or MO preference. Data tells us this is not true.
If you take away nothing else I write here, it's that a predator's reality often falls short of his fantasy. They may hunt for their "type" but who they had in mind and who they ultimately selected may not match at all. In the hunt, only one criteria mattered: she was available. One LE official is quoted in the article as saying "it's no wonder we didn't catch that many rapists because there was no pattern."
Finally, IMO the crime that may ultimately link to BG and Delphi may not be a stranger type abduction/rape.
It might be an acquaintance rape, which are notoriously under-investigated. Over 80% of rapes are believed to be acquaintance rapes...which is not to say that Abby and Libby knew their attacker. Historically, investigators thought that the type of person who assaults an acquaintance is very different than one who abducts/rapes a stranger in an alley. New data from the backlog of rape kits tells us that there is not such a gap at all. Testing the acquaintance rape kits turned up links to serial offenses on strangers a high percentage of the time.
To sum up, just like genealogical linkage is imperfect because not everybody opts in, CODIS is imperfect because of all of this missing data from sexual offenses. Hopefully in time that DNA link will turn up. I choose to believe it will. Perhaps a good use of our time would be advocating our local governments for testing the backlog of rape kits in every state.