I can definitely understand why the idea of PC being guilty is easier to believe than that of LC. PC just sounds cold and indifferent whereas LC was by all accounts a loving mother prior to this happening.
But the fact that PC is clearly a very cold, unfeeling man doesn’t mean that he murdered his children, I struggle to see what his motive would be when he could just walk away with his new woman. And if he is a psychopath/sociopath who killed his children, wouldn’t he make a show of being completely brokenhearted?
I think it’s more likely that it was LC who killed her DC, as she is claiming. But I think it’s likely that she was indeed mentally ill with PPP at the time, so she isn’t guilty of murder.
If it was LC killing them when in a state of psychosis, then PC is more guilty morally than she is IMO. Because he left her alone with the children when he must have known how unwell she was.
The fact that she might not have seemed to be mentally ill just afterwards is irrelevant. I had very bad PTSD symptoms for years, with distressing flashbacks, because of my childhood CSA. No one had any inkling, as I was able to hide it completely and function normally. (Not from my DH, though.)
I haven’t followed the case closely, just this thread, so I might obviously be completely wrong. I’m not saying that it’s certain that it wasn't PC who did it, just that I think of was more likely to have been LC.