Peter Kurz appears on a surveillance photograph biking in Manhattan when he claims to be in Brooklyn, and this should already raise an eyebrow. Motivated by the fear that Lorenzo would out him as a faux-environmentalist (he imports produce from Italy and also is a fan of toxic chemical management), Peter stabs Lorenzo through a back entrance. He does so with a wooden knife of his own making, as indicated by the strange smells, which he then burns by throwing it into the oven through the pastry room. You know he carves knives from his magazine story, and Charles notes a strange smell in the kitchen after the murder.