I am afraid he might kill her

I'm not sure whether my neighbours are lawfully married or how long they have been together but their first born is about 10 years.

The lady seems to be a good person but her husband is such a snob, from the way he behaves. He never greets. Even when you meet him in his car in those small estate roads, he can never give way. All he does is to raise his car windows and you find your way.

I would never expect such a proud and educated man to beat up his wife in the presence of her children.

He beats her very often almost the whole night. All the neighbours are so fed up.

What should we do?

Please don't tell me to mind my own business because this guy might kill her.