Be a great witness.
A tactic I have used in some less dramatic cases. Use a video camera. Most recently, I Had some 10-13 year old types jumping my fence stealing fruit, and throwing it at the house and fence.
Took the video and "filmed" the "little darlings". When I spoke to the parents, the kids of course lied. You could tell, easily, their lips were moving. Denied everything and of course accused me of not liking kids.
As is most often in todays society, parents take the side of their kids instead of the adults and/or teachers.
Most of the parents just shut up and were embarrassed when I showed them the Video of their "little darlings" doing what they just said their kids "would never do". The better of the group immediately handled the kids, and apologized. A couple actually tried to deny the video they were watching. You know that most American of diseases, DENIAL.
I advised the parents that if there was any damage or police involvement in the future, the video would find it's way into police hands. Pretty much solved the problem.
AS to being armed, if I am up and about, inside or out, I am armed, CCW. This was not a "defense" situation, and no need to turn it into one.
Remember there are only two types of problems in the world, "theirs and mine". And it's my job to make sure their problem, remains their problem. That doesn't mean, don't assist or help as you see fit and are able, just keep their problem theirs as you assist and help them.
Simply amazing.
Go figure.
Fred