I wonder if love possibly exists even if a child does something absolutely terrible whilst at the same time the parents can't forgive what they've done, or maintain contact? But the love, rather than being unconditional, as such, is based on who they were rather than who they are, and a hope that maybe that person they were, or you thought they were is still in there.
Maybe it's hopeful love. Maybe a belief they can't be all bad because you remember when they were a toddler giving you hugs (if that was the case). Then there might be guilt-"what did I do wrong?"
I don't know, never been in that situation, but maybe for some mothers, the love is simply a memory they hold that they can't let go? Of a child before the murder, or whatever, or of those moments, evening if fleeting, when little Johnny seemed like any other little boy.
I remember the parents of one of the Bulger boys saying they had no sign he'd do anything like this. I wonder if, particularly when a child is still young when they do an awful thing, it's really not that you love them no matter what they do, but that the love you have before they do it isn't so easily erased? I read somewhere that some parents in that situation feel like their child died. The love is still there, but it's for a person who isn't there any more.
Could be I have just waffled utter rubbish, but it's quite an interesting topic.