I'm tired of being part of the murder of the guilty on a systemic level. No crime is heinous enough for me to say "Yeah, government, go ahead and murder us".

Absolutely, I can understand why he would say he felt sorry for the family. But saying sorry for the pain he caused is an admission of guilt.

I think the timeline went like this:

• 1990 Brewer (then 19) and his girlfriend attack Laminack, killing him.
• 1991 Brewer is convicted and sentenced to death.
• 2007 Supreme Court overturns the decision because of a technicality on the jurors' instructions.
• 2009 Brewer is re-tried, and again convicted, in part due to expert testimony from Coons.
• 2010 In another trial, Coons' testimony was ruled as "insufficiently reliable".
• Brewer's lawyer then raises an appeal in Texas over Coons' testimony in 2009. Appeals court says "you should've said that in 2009".
• Brewer's lawyers escalate to the Supreme Court, however they decline to hear the case, deferring to the Texas Appeals Court's judgement.

Presumably, Coons' testimony could have been challenged in 2009 in exactly the same way as it was in 2010, but they didn't do this. I'm sure Coons is now seen as an unreliable witness, but he was considered reliable up until 2010.

It was actually the Texas Appeals Court that ruled that Coons was unreliable, however presumably the appeal in which they established that was granted for other reasons than his statement alone. Indeed, this is the 2010 case, there were 25 points in question. While the court ruled that Coons' testimony was unreliable, they still reaffirmed the conviction.

That didn't matter in the death sentence appeal where the court ruled the testimony as unreliable: https://law.justia.com/cases/texas/court-of-criminal-appeals/2010/20229.html

They ruled that the testimony was unreliable, but still let the sentence stand. If all Brewer was arguing was the testimony, then the court would have reached the same conclusion.