It's just like with the Laci Peterson or Caylee Anthony cases... you can think there's been a murder all you want, but unless you find a body, you haven't actually proven that a murder has occurred.
It's more like when you go to bed and there's no snow on the ground and when you wake up there is snow on the ground. You don't have to see it snow to know that while you were sleeping it snowed. Hernandez would have you believe that it's possible that someone came in and covered the ground with snow. It's certainly possible, but unless you got some reason to believe that happened, it's not reasonable.