Warbreaker - Claude the Lifeless

Vacher ends up killing our steel who is then turned into the character that we do meet, Claude the lifeless. This is kind of a mystery. How did you kill him? And it's a fair question because seemingly from what we know, Denth and our steel are of equal ability and skill when it comes to sword fighting. Like no disrespect to Vacher. He's very talented, very old, but just not on the same plane level.