As a long time geocacher, can I share some thoughts and a story that is probably not going to help at all?
Story - it's long winded and I'm sorry:
I was caching with my husband and friends back in 2009 in Santa Barbara, CA. We are from NY and were visiting CA and did not know the streets or area. We saw there was a cache at the gates of Neverland Ranch and one right down the road called "Troll under the bridge". We found the Neverland cache and signed the log - each cache has a sheet or piece of paper which you sign your handle under the last person and then put the date down. We then sealed it back up and hid it again for the next cacher. We went to head down the street for the other cache but we saw it was under a bridge with water flowing. It was rated higher in difficulty and there was a bicycle at the trail entrance. We figured someone was already there and didn't know if it were a "Muggle" (someone who does not cache and would find us suspicious/disturb the cache after we left) and we didn't want to piggyback their find (walk up on someone who has found it and just sign the log without doing the searching or helping) and it was getting late so we decided to skip it and we left town.
Well, we got phone calls two days later from the Santa Barbara PD. They asked us if we were Ursamajr and (friends handles) which was odd since Geocaching is anonymous unless you put your name in you profile. They had contacted Geocaching and received our info because they found a missing boy deceased at the "Troll under the bridge" cache. If we had decided to get that cache we would have found him. He had signed the log for the Neverland cache right before we did and they wanted to know if we were involved somehow.
Thoughts:
If Abby and Libby were Geocaching they would know by checking the log and they probably would investigate the other names above or below theirs and names on caches in the area. I think they also would know if they were Geocachers because I'm sure their parents would know; there aren't many caches in Delphi, they would need to be driven since they are spread out (i will attach a pic of geocaches in the area); they would find the App on Libby's phone.
I just checked and the Highbridge cache has been reactivated. It had been disabled after their deaths. The comments are pretty interesting and will give you a feel for the area and bridge - also a good feel for the other trails in the area. In the latest log, the geocacher says they tried but the bridge but they were both to chicken to cross.
Anyway, I hope this wasn't too meaningless.
Image attached and the Highbridge cache is all the way on the right.