Blackout's crime is the motivation for Ta'harok's entering of the Original Universe, besides his tracking down of Caiaphus. No record of the crime exists. Basically, SM Blackout is responsible for creating the Ta'har. However, the Great Beings were angry with Blackout because he made them too strong. As a result, they forced him to weaken the Ta'har.
Ta'harok's logic is rather flawed. Firstly, the Ta'har are still stronger then they were before Blackout's tampering. Secondly, the main Blackout (Who Ta'harok was fighting against) is not the same Blackout as the one who committed the "crime". Thirdly, if the Ta'har have turned out better from the whole experience, is it really a crime?
Ta'harok has only ever talked about it in depth once, in a conversation with Caiaphus. The oration goes as follows:
|“||Billons of years ago, in my reality, a peaceful race existed. they were called the Gregreth'Nar. one day, a Scientist called Blackout mutated us... made us more powerful, to follow in his design. we thought of him as a god... he gave us weapons to wage wars, powers to fight powerful enemies, an armada of battleships, and a homeplanet, Tybion. we conquered our galaxy and we were proud and noble race!
But then the Great Beings got angry... furious for we had destroyed what they created. they called on Blackout to make us weaker again.. which he did. We lost our planets, our people were slaughtered.... we were being slaved by the races that we forced into slavery!
So, I decided to seek revenge against him. I came to this reality. To destroy him. He may not have our Blackout's memories... but he is Blackout. That is good enough for us. I found some of his DNA on the ship of a being called "Yon" . I used it to mutate me back to my powerful state, but there was only enough DNA for me.
So I came to this reality.. to seek revenge. Haha.... i suppose you could say that it was...
It is unknown whether or not this "billions of years ago" refers to an exaggeration of the amount of years that the Ta'har have existed, an actual amount of time (which would conflict with the established Timeline), or a display of how time passes differently in the SM Universe.