LE may believe Kyron is alive, but a competent investigation would not ignore the possibility that he is not.
A competent investigation would not put all of its eggs in one basket at this stage of the game.
If you google Paul Shuman-Moore, he was a college student at a small but highly prestigious liberal arts college in Iowa. He disappeared from campus and his body wasn't discovered for about seven months.
At the time of his disappearance, his family was absolutely adamant that he would never have considered nor committed suicide.
On the ground, though, that was the prevailing theory. He had made statements to other students on campus that could be interpreted as suicidal (or, to be fair, just the sort of black thoughts that some college kids talk about) and he left a journal behind which contained similar statements.
He even speculated to friends about someone committing suicide via drowning in a pool that was closed for the winter.
And indeed, he was found under the cover of a pool that had been closed for the winter. That pool had been checked during the active search. The tarp covering was old and had many tears and rips in it. It was huge and took a team of 10-12 workers to remove fully, so the searchers just opened one corner and looked inside.
In deference to the feelings of the family, LE and the media continued to say that they believed there was a chance this kid had walked away from his life.
I don't think anyone outside of his family was surprised when his body was found, though.
At this point in Kyron's disappearance, it cannot hurt to keep hope alive that he is still alive. There is, as we all know, a small chance that he is alive.
But there can be a difference in emphasis between what LE says and the actual focus of an investigation.