Regarding victims saying the perp had no accent, I initially thought maybe they didn't notice an accent because he was local, but that's not true. I have an accent and recognise when people come from where I am from, or even a neighbouring borough.
Having just made the thread about Patsy Morris, her father stated that after her death, I think after her body was found, he received a threatening phone call from a boy with a local accent. People do notice.
So I am thinking he had a neutral accent in some way. Maybe RP as is often hears on tv. I recall many actors stating when going to RADA, they were told to lose their accent.
Is there anywhere in the UK where an accent is close to being neutral?
Don't we also pick up how we talk from our parents and influential adults in our upbringing? I just spoke to a friend's daughter on the phone yesterday and she sounded identical to her mother.