Okay, take this how you want to, because I'm not verified. I'd like to protect my own privacy.
I am close to a case here. It was an abduction and murder. Sadly, I was able to escape but the next victim was not.
LE did not know where the victim's body was located, so the case took years to prosecute. HOWEVER, because of witnesses who saw the attempt with me, LE was able to find out who the suspect was relatively quickly. In public, they never let on that they knew who did this, and myself and others kept our mouths shut outside of LE and FBI offices. The case took years to prosecute because LE wanted her body.
I'm just giving this example, because in that situation, I feel like people said the same things... That LE didn't know what happened, etc. They did, but they wanted justice! They weren't going to lay their cards out for everyone so that monster could walk.