crime and punishment: there is no evidence to suggest that Kristen EVER left her bed that night. Yes, inmate lied about which child he found in the bed. I believe the reason is twofold:

(1) he didn't want anyone to know Kimmie had been in the Master bedroom
AND
(2) his own ego made it important that Kimmie NOT be the one who wet the bed.

I realize it may seem weird, but in his psych diagnostics it shows that what other people think about him is important. I believe he thought that Kimmie was too old to still be wetting the bed, that it was unacceptable that anyone outside the family know that she still did wet the bed. Plus, he did not yet realize that the entire family had different ABO blood groups. That anomaly allowed the CID and FBI to read the crime scene clearly.