An Assassin
The Inanis Family mansion was a secure location that was hard to infiltrate.
Its servants were loyal to the Inanis and could not be bought and the personal forces that they held were also a pain to deal with.
If anything, it was much better to avoid all of the guards if you could and not run into servants at all because the fewer people involved then the better your chances of succeeding.
Of course, that was difficult in itself.
The patrols of both the guards and the servants who resided within the Inanis mansion were numerous and were coordinated carefully so that not one corridor of the mansion was left unoccupied by at least two people.
It was never going to be an easy task, but the assassin managed to do what might have been the impossible.
Not because he was smarter or better than other assassins who could have tried to do the same and ended up failing, but it was because of the gift that the assassin had with him.