Replaying the MSQ in NG+, in HW, when you and Raubahn confront meriel the former maid of Nanamo, Lolorito shows up and explains the scheme to you. He said Ilberd knows full well of his plan to sabotage Teledji's. And he asked Ilberd to lie about the assassination to enrage Raubahn to cut down Teledji. What I don't understand is what's the reason Ilberd said to Raubahn after his arm got cut off (at the time Teledji's already dead) that he is the one assassinated the sultana himself which further enrages him and sparks the fight and later attempt to execute him.
Ilberd's goal has ever been fixated on liberating Ala Mhigo, what will he gain from defeating and killing Raubahn though? Simply out of hatred towards the "sultana's lap dog"?