The day before the murder happened, that official was seen arguing with one of the commander in Athena army about unfair distribution resources and the Athena commander was accusing the official to be channeling the resources to other secret project without consulting Death Monarch and the other factions in the court.
And the Sina faction accuses that Athena faction orchestrated the murder in the Palace.
The one that was murdered was an old man with only Orb Condensing realm but he was the leading figure form the political faction in the Central Government.
Athena of course did not order such thing.
She might be upset having to deal with unfair distribution but she would not have resorted to murdering her political rivals.
Not to mention she was not desperate for the resources since she takes over the West. She was prepared to investigate the claims when something else happen that push both parties into hostile position.