That is a tough one. I don't think I'd ever argue in favour of capital punishment, but there are times when it is applied as a punishment, and I couldn't honestly argue against it. I think this is one of those times.
Killing some one as a punishment is not unreasonable in many circumstances so in principle I don't have an issue with death itself.
However, the issue for me is the police are known to make mistakes, lie and create evidence and judges, juries, witnesses and lawyers can make errors in judgement for a variety of reasons.
In this specific case, I have no doubt the judge would have had politicians whisper in his ear the importance of making "the right" decision to avoid riots and deliver to the community what they want.
They probably are guilty and certainly deserve to die if guilty but the concept of a death penalty needs to be considered more broadly rather than a specific case. On the basis of the potential for error, I do not support the death penalty.