Someone just posted the evidence of this on the Something Awful forums. Halsin's diary indicates that he used a glaive to kill Isobel, and that this is why Ketheric went the way he did. Dramatic difference.
Yeah it was datamined years ago and I was actually REALLY looking forward seeing a darker side of Halsin :,(
Doesn't necessarily mean he had to be secretly evil, just a tad more complex.
