LE may well have a POI. Just because they haven't named one doesn't mean they don't have one nor does it mean they presently think that person is innocent, far from it.
So, on the hypothetical stand, the LEO wouldn't be explaining why he or she believed the person was innocent during the period we're in now but rather would testify to work product. When and how the person became their POI, what investigative steps were taken, what evidence was collected, etc.
I don't think LE is lost right now. In fact I suspect they are laser-focused. Gathering evidence so that an arrest, when it comes, can reach BARD at trial.
From experience here at WS, if LE thought there was a 1% chance those precious children might still be alive, they'd be leading the campaign to get the word out.
JMO