I don't think the issue was getting him to confess earlier, I think the issue is that LE "forgot" about him. The circumstantial evidence that Heinrich was Jacob's abductor was very significant. Additionally, there was physical evidence in Jared's case, in the form of fibers in his car matching fibers from Jared's clothing. The bottom line, IMO, is that they knew or should have known that Heinrich was the abductor. Proving it, yes that's another matter. Going after someone else, namely Rassier, was baseless IMO. The whole claim about waiting for science to evolve to nab Heinrich severely contradicts the actions that Stearns committed against DR.
I agree with your prior point that perhaps the In The Dark series may have jumped the gun on some conclusions, as future releases of investigative files may shed new light and fill some holes. However, I know first hand how thorough Madeleine Baran was with her research into this. There are many, many things she left out of the podcasts that weren't quite certainties. I believe time will show the series will be highly accurate in its conclusions.