I am not so sure the parents didn't blame her. As a matter of fact I think JS and probably DS DID blame her, which is why she was so distraught.
He should not have been allowed to run and jump around at the top of that dangerous staircase. End of story. And accident or not, that is what he was doing. He should not have been allowed to play up there all alone, totally unsupervised, if he did not have the self control necessary to avoid such a tragic outcome. This was a dangerous, un-child proofed home. I would not have left a 6 yr old alone at the top of those stairs.