A good point. The "hiding in plain sight" aspect. If this killer is currently local - local being anywhere within an hour or so of Delphi - perhaps the problem with the DNA is they have TOO MANY possibilities.
I know if I go to the mid-west where my parents' families are from there are MANY in the county and surrounding counties who have some relationship to me. I remember once while in a community an hour away from where I was visiting I came across two brothers and one of their cousins with the same last name as myself. And my last name is very UNCOMMON as it is an Anglicized version of a European name. I didn't know any of them and they didn't know me. Later when I asked my parents, grandparents and aunts/uncles, they had no clue as to the relationship to us. But they said it wasn't unusual either as this area of the country was where the name originated. Had someone obtained DNA they would find family matches across the state and at least two other neighboring states.
If this killer is from a family or families with generations in central IN this might be a problem in itself. I do remember that one point a few individuals came forward and stated they provided DNA swabs to LE. Maybe one or more of such individuals have some very distant - e.g., third, fourth or fifth cousin - to this killer. Too distant for LE to be able to make the connection. AND if LE doesn't even know if it is the killer's DNA, then that just complicates things further.
I don't think it is legal for LE to use swabs from individuals who submitted DNA in order to clear themselves to do the genetic genealogy comparisons suggested in this post. In my understanding, if any individual submits a DNA swab for comparison in Indiana it can only be compared to the sample from the crime scene for purposes of identification and it is not retained if no direct match is found. I do not believe that it would be legal for Indiana to allow LE to then keep those samples and compare to other cases or to calculate kinship to unidentified samples. Indiana doesn't even allow familial analysis of samples from known criminals in state databases so I doubt this would be allowed for people who have never been convicted or accused of crimes who are submitting DNA voluntarily. All MOO though.