I found it curious how Zach said he didn't remember his baby sister, just the blood and how his parents said it wasn't his fault. He didn't say anything about his baby sister as a person, and it happened around the time he was four, about the time that infantile amnesia kicks in.Zack sounded like HE was guessing at what the big mystery was, too.
I wonder if the "baby" everyone is referring to is Zack (i.e. nosy old lady talking about what Mary Alice did to "that poor baby").
If the old bag supposedly knew the truth, and she must have for whatsisface to kill her, then Zach's theory that he killed the baby must be wrong, right?
So Zach remembers a pool of blood, his mother telling him it wasn't his fault, there's adult bones in the box, and it was indeed Mary Ellis who did something.
Could the bones be another person who found out the truth prior to the nosy neighbour?
I'm getting more and more convinced that Zach is the baby that something bad happened to, although that doesn't explain the "Dana" name embroidered on the blankie.
Incessant whining.