Seems unlikely to me that 20% of the population were connected to a terrorist attack by someone who would be executed.
Even if, I don't see how seeing one of the perpetrators getting killed many years later would give relief.
I also believe eternal prison is a bigger punishment than execution.
Not by the same one that is going to be executed.
He spent his life in prison, now he would be executed live, everyone would see how he's going to die, and for him at least, it's very disrespecting.