A couple of posters have postulated that two knives were used. If they are thinking one knife in each hand, that is hard to do. Most people handle a tool in one hand, not handling a tool in each hand. To use a knife in each hand, and use them effectively in a combative engagement, requires training. Most people are not that physically coordinated. ("Most" is an analytical qualifier. For example, "most people" cannot run a four minute mile, but there are some who can.)
For several years, I did a survey of military and security personal combat from the 20th century, and for the most part, the knife work is done with one knife in one hand. There are some traditional "martial arts" disciplines that use two knives, but these are a minority.