So having beat the main-quest of Morrowind a couple times, I always thought it was fairly clear-cut that the Tribunal were responsible for Nerrevar's death. I played through it again this time, however, and in talking to Vivec, realized just how convincing Vivec made it sound that they really weren't responsible. The game seems to leave the question open, but do we really know for sure how Nerrevar died?

Vivec the mortal killed Nerevar, Vivec the god did not.

Small wonder Aka hates us.

It was Vehk, Seht, and Alma. They all played a part.

By what reference do we know this for certain?

Well, when you're being beaten over the head by puny mortals, I guess that'd make ya angry. He doesn't want to be second bananas to a bunch of 'lesser spirits' who are riding motorcycles around him, while shooting the bird at his face and smoking!

http://www.imperial-library.info/content/morrowind-nerevar-red-mountain, Vivec's confession validates it to an extent.

We don't know that Almalexia and Sotha Sil actually helped. Some of the stories say they did, but as far as I know, Vivec never incriminated them, or gave any indication that they had anything to do with Nerevar's death. They did betray him in breaking their oaths, but I've never seen anything suggesting that Almalexia and Sotha Sil helped kill Nerevar.

True. I just get the feeling Vivec didn't act alone in murdering Nerevar.

One question that has always bugged me: Why did the Tribunal do what they did? Did they lust for power, but upon achieving godhood, become enlightened to an extent that they used their powers for the good of Morrowind? Or was it a feeling that Nerevar was blind to the opportunity of utilizing the Heart's power to bring peace to Morrowind? Or was it something else?

Vivec admitted to killing Nerevar at the Trial, while wearing his Water Face (meaning he could not lie). Of course, his defense was that the murdering mortal no longer exists, and the god does.