I can't really see how people can say he was rehabilitated.
He never apologized for the crimes he was sentenced for. He always maintained his innocence, so fair enough, but then it's a question of whether or not you believe the (considerable) evidence against him. And if you believe the evidence, then his failure to admit and apologize for his crimes must surely weigh heavily against him.
He expressed regret for founding the Crips gang but refused to give police any information that could have helped them arrest and prosecute members of the Crips.
He wrote (actually co-wrote) some children's books deploring gangs and gang violence.
You can read the LA County DA's (lengthy) response to Tookie's clemency petition
here, which includes a review of the evidence which convicted him.
I can respect those who oppose the death sentence as a matter of principle. I have a harder time with those who claim Tookie was innocent or rehabilitated.
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The Ottawa Citizen and Southam News wish to apologize for our apology to Mark Steyn, published Oct. 22. In correcting the incorrect statements about Mr. Steyn published Oct. 15, we incorrectly published the incorrect correction. We accept and regret that our original regrets were unacceptable and we apologize to Mr. Steyn for any distress caused by our previous apology.