Answer:
Catachresis
Step-by-step explanation:
Catachresis is the figure of speech used to improperly use words or terms in sentences because there is no other specific word for what the author expresses.
In relation to the sentence shown in the question above, we can see the use of Catachresis in the term "ax murders", which is the improper term to express "deaths caused by the use of an ax."