The Wikipedia article is a good start.
If you have anything like OnDemand do a search for Menendez and see which documentaries pop up on your cable service. Over the years there have been several tv shows done on the case, many are documentary style going over the facts (usually with bias, of course) and others dramatize the events so it plays out like a movie. YouTube should have some of the shows too.
Basically there are two camps: Those who believe the brothers killed their parents for their inheritance, and those who believe the brothers were sexually and emotionally abused by their parents so they killed them to stop the abuse. The latter was their defense at trial.