Yup. He's toast!
Plus, if they found the rest of the body and home-made concrete boat anchors were used -- which he admitted making -- that's all for him. It's 'Let's Make a Deal' time. "Well Scott, are you going to confess and take life without parole, or do you want what's behind Door #1?"
I'll bet the prosecuters won't want to make a deal, , no need to, they got him cold!