It's interesting that, as best I recall, Konrad never denies any of the General's allegations. Nor does he show remorse or ask forgiveness. If the General was not seeing reality correctly, you would think Konrad would make some comment in his own defence.
Krisztina may have felt these things. That may be why she called for the General from her death bed.
The General expresses guilt - at least toward the way he treated Krisztina.
But Konrad expresses nothing at all.
Well, Konrad does present a puzzle that needs explanation.
One of the structural features of the novel that I only realized during reread seems to be the fact (as I read it) that
none of the characters is aware, for a fact, of what the other characters knows or thinks. The General, by himself, pieces together what must have happened, but he doesn't
know for sure. He only has logical conclusions. Which is why he asks Konrad if Krisztina knew before hand what Konrad was intending. An answer would have given him his first
factual corroboration, one way or the other, of what he has been thinking. But Konrad won't answer, so the General still doesn't know for sure.
Krisztina doesn't know whether there might have been any conversation between Konrad and the General before Konrad disappeared. And the General doesn't wish to raise the topic with her, to allow her to keep her self-respect (or words to that effect). So she finishes her days not knowing at all what happened in the woods or at the end or how much the General knew.
And Konrad has been away, so he definitely doesn't know of the General's or Krisztina's visit to his apartment, or what the General has concluded in his thinking. And in fact, the General never actually
saw Konrad taking aim at him (he only sensed and deduced it, as I reread it), so Konrad never knew that the general had sensed that he had aimed his gun at him. He found out for the first time during the monologue, the way I read it.
Konrad returns, according to the book, only for the vague reason to resolve an open issue in his life, without saying what that was or how he was going to do that. Initially, he seems unaware that the General has deciphered the events and he claims he left no debts behind when he left and he presents himself as having done nothing wrong in leaving. The General says not so, and proceeds to tell him of his analysis. Which seems to take Konrad by surprise. So, yes, as you say Konrad is left with no defense and does not challenge the General.
I guess that convicts him. But the premise of hatred still seems far-fetched to me. The General says he should have known it when they were cadets and Konrad declined to accept any of the General's money or other offers of gifts. "He who won't accept any part, wants the whole" is the way the General puts it, and that leads to hatred, as I recall. I can't accept that. In the case of Konrad I suppose the story tells us it leads to a lucky hit. But in general I think the notion is far-fetched and as fictional as the story.