As far as I can tell, we haven't figured out what caused her death yet, or the actual weapon used to kill her. We know there's a letter opener missing and some knives from the kitchen, but she died from puncture wounds.

[ he crosses his arms. ]

I won't pretend I can tell what was used just from looking at her injuries. But I'm pretty sure carving knives and letter openers wouldn't typically leave puncture wounds.