Could murder be modeled as an infectious disease?
Disclaimer: I'm an infectious disease modeler, and generally pretty skeptical of "We modeled X like an outbreak!" claims, because many are just an exercise in curve fitting.

Given that, the answer is both "Yes" and "No".

"No": Murder as an act really isn't transmissible, and if its not transmissible, it can't be modeled as an infectious disease.

"Yes": It is probably possible to model some things in the same way we model infectious diseases, because the underlying causes of murder may be somewhat 'transmissible'. Certain behaviors, cascading effects (if one family member is incarcerated it increases the likelihood that other members of that family will be incarcerated) etc. might give crime "disease-like" properties.

That's probably largely driven by underlying social networks and the like, which are also important to infectious diseases. But then you have a problem in reasoning. For example, did murder "spread" along a social network, or did we merely sample a group of people with a shared underlying cause (for example, poverty, membership in gangs, etc.)

It's probably useful to model some of these things, but it's more useful, in my mind, to model them as their own process, rather than trying to shoehorn them into being like a disease.