EVERYONE with a knife has the potential to be deadly.
Edged-weapons rarely fail. Blades do not have a “line of fire”, as most of what is exposed is dangerous, and blades, once presented, are always live.
Edged-weapons, unlike firearms, are often weapons of convenience, gleaned from the environment during a violent encounter, and are therefore more prevalent: knife, screwdriver, scissors, pen, and more.
The dirty little secret is, you do not need to be skilled with a knife to do massive damage.
What you need, is intent.