I don't think he clearly made it up. Not if you read his confession transcripts. He seems to be telling the truth to me.
And how can you be so sure the evidence was planted?
Well, it does if you believe the police would be able to plant all those things. I suppose they could have done, but then his sweat was on the key. Do the police have access to his sweat? It seems a bit far fetched to me.
So not the key or the blood in her car or the bones in his yard and the fact that he was the last person to see her alive? Oh and the bullet too that was a match for his gun