What I find most dreadful in the barbarism that is state-sponsored murder, is the notion that the state is keen to ensure that the prisoner understands why they are being executed.
What on earth difference does that make?
The prisoner is unlikely to say "Yes, I understand, go right on ahead ..." are they? So why does their 'understanding' make any difference whatsoever?
Maybe the state is trying to salve its collective conscience in attempting to obtain complicity from the prisoner, although again, I utterly fail to see why this makes any difference - the state wishes to murder you, and it will, whether you 'understand why' or not.
Some of the answers refer to the gravity of the crime, and there is no escaping that this was a horrific situation - but to use that to justify an execution makes that revenge, and revenge and justice are not the same thing.