In order to prove that evil deeds are afoot in Eorlsmead Tower, evidence must be gathered.
'Gadda's concerns are well-founded. There is much going on here that Stanric could not have known about when he was alive, for I am sure he would not have approved. I can let you explore the tower, but I fear to rouse the suspicion of my peers.
'There is much evidence here of Sithric's dire corruption. Find any such evidence you can and bring it back to Gadda; hopefully, it will aid his cause.'
There is likely evidence of betrayal somewhere in the tower.
You should collect any evidence you find in the tower.
Swithulf is at the Eorlsmead Tower.
You should speak with Swithulf and confirm the evidence you have collected.