In regards to Lee, I don't feel he had anything to do with whatever happened to Caylee. Casey and Casey alone is responsible for Caylee's death.
When Casey called home from jail the night of July 16th, Lee was firm with her, telling Casey that he's "not going to be put through what she's put mom through for the past month." He tells her that they're going to find out the truth eventually. At this point, I think Lee honestly didn't know anything.
When LP posted bond and Casey came home under home confinement, he stated that Lee was initially helpful to them, turning over copies of the cell phone records and sharing what he knew with the bounty hunter team.
It was after the forensic results were announced and LP stated that he felt that Caylee was dead, that Lee refused a lie detector test and convinced his parents not to take one either.
I think at some point, Casey confided some details to Lee about what happened. Lee's refusal to take the lie-detector test may have been because he knew he would probably be asked if Casey told him what happened. If he answered that question truthfully, he would have to tell LE what he knows. If he lies, that will be noted, and he could be charged with being an accessory after the fact for concealing details of a crime. I think Lee may have told Cindy and George what Casey had confided to him, and they are therefore in the same position and refused the lie detector tests too.
We don't know if the post on CL is true, but if it is, it may be a factor in why he's withdrawn. He may feel he can no longer support Casey's lies, and is focusing on his own life.