At the end of the first season of Carnival Row, we find out the true motive for the killings:
to find the illegitimate son of Chancellor Breakspear and kill him.
With that in mind, these murders and their order make perfect sense:
1. Aisling, because she's the mother of the said son and because the fake blackmail letter made her the first link towards her long lost son.
2. Finch, the headmaster of Philo's former orphanage, was the next target in that pursuit, because Aisling didn't know what became of her son, but she did know where he was left. The quest would've been over here, as he knew who the boy is, but his liver never made it to the murder, and she never got to learn his secrets.
3. Dr. Morange was another hint that came from Aisling, as he is the one who cut off the wings of her half-blood soon. It was quite obvious that he didn't know the secret either (he never showed Philo that he knew), so that was a dead end too.
5. Chancellor Breakspear('s liver) finally provided the answer.
What I don't understand is why was it necessary to kill
4. Aoife (Haruspex)?
She is the closest thing to a friend that the murderer has, she didn't know anything really important at that point, she said she'd learn who the culprit is just before her death,... so, why kill her? It feels that, without her death, the murderer would've probably succeeded, as Aoife is the one who told Philo who to look for and that she has Vignette.
What am I missing?