What term would you use for a person who caused an incident

A neutral term for this would be principal:

[Merriam-Webster]
noun
1 : a person who has controlling authority or is in a leading position: such as
e : the person primarily or ultimately liable on a legal obligation

In other words:

Who was the principal of the incident.

Admittedly, it's not an entirely common use of the word, but it's still acceptable.


It could also be used adjectivally, a form that would be more common:

Who was principally involved in the incident?

This, too, uses neutral wording.