I don't know all the details, but it would appear that five people disappeared simultaneously late one Saturday night. I would imagine that, on Sunday afternoon, at least some mobile phones would still be working. By Monday morning, maybe not. So the police may have had an opportunity on the Sunday to find those people, that was lost by Monday.
A lot of things are tragic about this. For example, did some of the deaths be preventable had they been found sooner? And how awful must it have been for the two who did not die.
It definitely needs investigating.
With several of my family members, I can track their locations through Google (other providers are available). However, I can understand why young people would not want older people to do that, which is why only the police could really have helped here.