At least make him swear this was the knife which killed two people.
Sickest part of the whole situation - who cares?
No matter what he says or signs, he can't be prosecuted for murder (double jeopardy). And the Goldman's have already sued. Basically he can come out and say almost anything related to that crime, and face no additional sanctions (unless some of the inmates decide to settle things themselves).
Pretty pathetic.