From Halloween To Scream, the most recognisable slasher killers (Michael Myers off Halloween, Ghostface off Scream and many others), an average kitchen knife is the killers' choice of weapon.
The above picture is very similar to the knife we use in our production, we used it because Halloween and Scream are the two most influential slasher movies to us, and the choice of weapon from our killer needs to adhere to their codes and conventions.
"In John Carpenter’s era-defining slasher movie, the weapon is just your average, run-of-the-mill kitchen knife. Nothing out of the ordinary. But in the hands of a crazed mental patient in a William Shatner mask it becomes oh so much more." - Quote taken from http://www.scene-stealers.com/top-10s/top-10-instruments-of-death-in-slasher-films/