There is a good article in Vanity Fair by Nick Bilton, who attended the trial.
He did cause some deaths with his drugs and poison smuggling. Some government agents involved with him went to jail.
The sentence may seem harsh but the article does explain why. He was offered, and declined, a plea deal that would have been appropriate. If Trump grants clemency he should also grant clemency to the black kid that was sentenced during the lunch break of the trial.
This is more an indictment of our plea-bargain system which all too often is designed to discourage jury trials by offering a bitter but short prison term in exchange for pleading guilty while dangling draconian life sentences if you risk a trial. That's not justice. That's a mafia-style "offer you can't refuse."