[Kiltias]

Originally Posted by Renall

And nobody has an especially great reason to kill everyone.

What about killing everyone part the Servants?
As in the target being the Family, the servants being killed simply due to being servants, furniture, looked down upon by the culprit as well as wanting no survivors or simply to silence them.

Put yourself into the Culprit's shoes, would you keep them alive if you plan to kill the family?

Or for all we know it's like the A,B,C Murders from Agatha Christie.

Spoiler for ABC:

The Culprit in this was trying to pass a murder as a part of multiple murders, they killed 4 people in order to surpress the truth.
Alice Ascher
Betty Bernard
Carmichael Clark - The actual target the culprit wanted dead.
George Earlsfield

As in:

Spoiler for Perhaps:

What if the Culprit had some true targets as well among the victims but killed everyone to hide the truth behind the motive.