Theory...Here's mine, although I haven't read every post thus far, so some may be redundant.
I think they found Caylee to have been injured in some physical way to cause death, and that made them re-think their chloroform scenario. Where did it come from in the trunk? Pesticide, which can lower decomp smell, something well-known to le, according to Wendy Murphy. Was the trunk washed in pesticide by someone? They took the sprayers...I also believe we found, somewhere on these threads, pool chemicals can cause chloroform, they took pool chemicals...anyone recall?
I also think they found her in the same clothes as the gg video, or found some of that precise clothing (or maybe nightclothes,bedding), tying it to the 15th night, which then would show George to be lying about the 16th, hence the possible obstruction charges.
If the trunk is found to have been washed in pesticide, there is no innocent reason for that, imo. The purpose is evident to me, which shows intent, intent to destroy evidence.
AND, the searches on the computer for chloroform...episode 813 o CSI, which Lenny said she liked and was listed as a fave on her myspace, aired at the beginning of April/2008...I found a blog where it was previewed, and comments were made on March 21,2008, she did searches on the 21st. This episode involved a Child, a little girl, found in a bag with elevated levels of chloroform, caused by drain cleaner. That week, Casey had a very hard time with her social life, she didn't get to go out...and it was also her birthday week...
http://www.buddytv.com/articles/csi/csi-spoilers-for-episode-813-a-17760.aspx