NotJ - we have a lot more people on suspect list than just the obviously dodgy characters. Someone in the car isn't just someone , it's THE serial murderer.
Who could be the baker.
I think the baker fits the murderer profile for the two facts - he can get into someone's home without breaking any doors/windows which is the hallmark of all the murders. HOW did he get into all these flats? most people in London do not just open a door to unknowns. Must be someone v.experienced at picking the locks??And him supervising Cullen provides him with alibis (goes both ways). But I don't get it why did he break-in into the jogger's flat - to kill him but couldn't do it as he was stabbed - or just to steal.
Also I was typing my post late last night, but what I meant re copycat killings - whoever killed Grace did the copycat murder of those other ones, because it would be a huge coincidence that a random bloke would target Grace (priviledged, not founfd on any online pick-up/dating sites), as opposed to more 'common' people that the original murderer targeted - I'm 100% sure she was killed from someone she knew well, most likely to do with the business.
Whoever it was KNEW about the other/historic murders - possibly because they've seen pictures in Marcella's house - or they are involved in investigation! The obvious would be her H, as I thought before, but knowing now that he loved Grace and had a long affair and was crushed by her death - it was not him. Unless it was some dreadful accident - and he had to dispose of G's body and then dump M into her bath while she had a blackout. Not v.likely.
I'm still now thinking Grace was killed possibly by mother's partner - the only hitch with that is, how could he dump M back in her house. Both he and step brother know Jason's address but whoever did it must have known of the affair (step brother did) and must have heard the row to be sure that M is Jason's wife. But they didn't know about her blackouts! I think maybe she did NOT have a blackout that time, she had a horrid bruise on her head - so maybe she was just knocked on the head by Grace's killer and fainted.
Cullen - not the killer imo but he is already violent re BF - what's his plan though? to kill bf, or to let him go and in any case be sent to prison again? unless he just wants to hide him away to make it look to the girl that BF dumped her. But it's really weird that he'd want to likely go back to prison just after his release!
Parallel to that, the other newer murders could be either the original murderer returning OR a new one doing the copycat. Again would know the details - Cullen knew the details as he was a suspect so he could have told the baker - who then copied it to mislead the police.
So imo there are two or three murderers (Grace's one not the serial killer).