IMO, they didn't "send" the father home. He lives in a different state and had been in Iowa for a month searching for his missing daughter. He was likely exhausted and perhaps his funds were too. There is no script to follow when it comes to this, and there is a limit to what the father could actually DO while in Iowa.
The sad fact of life is....life goes on.
I don't think LE told the father to go home, but I'm sure they supported the idea for his own good. Anyone who supported or encouraged the decision did it out of kindness to the father, not because they wanted him gone for their own good.
LE had an ongoing investigation. They didn't pinpoint the suspect and interview him until after the father was gone. At that point, they had NO IDEA the suspect would confess and lead them to the body.
Of course it's heartbreaking, as you mention, the father wasn't there when LE broke the case. But the whole dang thing is heartbreaking. Coming up with conspiracy theories, imo, is taking advantage of a tragedy for sensational purposes, and that is unkind at best.
jmopinion