What is the most heinous crime that could or has been committed?

The Holocaust.

Genocide is heinous. Dropping the A-Bomb on civilian populations may have been the worst as it was sort of an instantaneous genocide and it's potential is horrific and almost limitless.

The Holocaust was terrible, but there have been many similar genocides so its hard to pick that particular one as the worst. The genocide of the Europeans against the Native Americans probably was greater in scope and final effect.

Purposefully destroying the entire earth (including all earthly life) is potentially the worst crime that could be committed, greater than crimes of killing only humans.

The Holocaust comes to mind first.Contrary to coyote dude there has never been quite like it in severity or what the stated goal was.

Right up there is the Supreme Court subverting our Constitution and appointing dumbya bush president.

September 11, 2001 was the worst in my opinion, maybe it is because I knew someone on one of the planes...

The Holocaust and genocide are also very high on my list of disgusting crimes.

any crime against humanity. whether it be sexism, racism, any kind of -ism. any of those are hate crimes driven by ignorance and done with malicious intent, i.e: toture, abuse, rape, murder, genocide, lynching. (just think of the famous hate crimes associated with those words) those things in themselves are horrible, but doing them with gratification because of hate is (in my opinion) the most heinous crime.

In my opinion it is sexual abuse against children. When found guilty the offender should be executed immediately. Rehabilitation is a joke with them and will only allow them to repeat their offense over and over again. Fry the bastards!

I think I will have to agree with George Clooney on this one.