You could only get the accident theory out there as one of several possibilities. Going the round about way you ask all the people who said in sworn statements that Casey was a great mother, would never harm her child, and some of them even said it would have been an accident and a cover up.
My only point with my previous post (because again I think she will be executed for killing her child, but my for the sake of arguement posts get quoted and then I have to answer all the "you have got to be kidding, the evidence is overwhelming" posts),
but all of the evidence we have seen can be spun in another direction:
Any body found 6 months after the fact you can and will see an expert on the stand giving a different window of time of death, or saying that it cannot be pinpointed to a window smaller than a month.
The evidence of a body being in the trunk, there is evidence that the car was with other people, that Casey was driving vehicles other than the Sunfire, Casey does not own that vehicle, etc....
Her actions after the fact can either be dealt with head on, my client is not a likable person, I am not asking you to like her or invite her over..... or you can take the route of the last verifiable siting is with Cindy on the 15th and that Casey was out and about for a month because she had finally given into Cindy's demands of custody.
I don't think any of that will work, but none of the evidence is black and white in front of a jury. There is room to work when you acknowledge he does not have to prove she didn't do it. If he manages to keep the initial statements out (just like you try to keep confessions out) that will be a major win on the defense side.
And again, I think she is guilty, I think the state has done a great job, I think she will die for her actions.