How could you boil someone?

A woman was boiled in the kitchen of her ex husband. This is the saddest gruesomest thing I have ever heard of. Her legs and arms were boiling in pots while her pelvis was in a bag already cooked. how could anyone even do that? This was actually in mexico I think.
http://www.foxnews.com/world/2018/01/23/womans-dismembered-body-found-boiled-on-kitchen-stove-cops-say.html