somequestions
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This was my thinking three years ago but my opinion on this has evolved.
My first assumption was: a crime like this (IMO it's a sexual homicide) MUST leave the offender's DNA. However, in a landmark study of child abduction murders, it was shown that a little more than half of cases yielded DNA evidence from the scene. My conclusion: it's not as common to have a perfect sample of a perpetrator's DNA as numerous tv shows and books would lead you to believe. In addition, the same article indicated that the presence of forensic evidence from a scene does not increase the solvability of a child abduction murder very much. Seems counter intuitive but the factor that accounted for most solved cases was LE being able to discover the relationship between victim and offender. And if LE couldn't do that? They had a very hard road ahead of them.
My second assumption: if BG has committed previous crimes, then his DNA is in the system. I'm starting to have a lot less confidence in this. There are about 4,000 untested rape kits in Indiana alone, for one thing. For another, have you noticed how many times cold cases are eventually solved by hits in CODIS but the time lapsed between the offender's crimes are really huge? A typical timeline might be: unsolved murder from 2003, convicted of second murder in 2008, samples finally matched 2014. Not sure what's going on with CODIS but it's not a perfect or quick matching system, that's for sure, though I grant you it's the best we have right now.
My third assumption: if detectives get a DNA match on a suspect then they immediately arrest him and it goes to trial where it's a slam dunk. I'm starting to question this. The standard guide for LE investigating child abduction murders (Brown & Keppel, 2012) states:
"Research has shown that most criminal investigations do not rely on forensic evidence as a means to solve the case, but to bolster the detectives' chance to use that evidence to obtain a confession from the suspect..."
If this is so, then the actions of LE in keeping DNA information close to the vest in the Delphi case becomes 100% clear.
I agree with the research. DNA is great, but you still need someone to connect it to. So people start to believe that since the case is not solved therefore there is no DNA evidence.
There comes a point where you need to be able to narrow the focus in any investigation. The most disappointing aspect of this case is that LE may end up chasing around sketches for years. And if nobody realizes they are wrong, the conclusion will always be that they just could not find the person in the sketch, no matter how much time passes by.