SPOILERS!! Please can someone explain the ending of the sixth window by Rachel abbott?? SPOILERS!

[DontFundHate]

So I've just finished it. But who killed Bernie gray?? And what's all that about the dog collar? I suspect it's Ed? But am I missing something? Thank you!

Read it ages ago but isn’t it that the bloke could only know about the collar if he had been the one who ran them over? As it was new that day.

Yes that's what I thought! So Ed did kill him? But Bernie was helping a peado so that's ok?? And who was it who asked Lewis to send them Scarlett's photos? Was it Alison? I had assumed it was a man until I got to the end of the book???