During the War of the Ancients, Illidan had seen five humans. A Bronze Dragonflight had sent them to that era, and they had participated in the event supposedly to preserve the Timeline's proper course.
After the Well of Eternity was detonated, the five vanished from where they stood. The Bronze Dragonflight member had even tried to erase Illidan's memories, only to be driven off on the spot by a Mana Burn and Immolation combo.
Illidan had not thought much about it at the time. He had been preparing to take the seven vials of water he had hidden to Mount Hyjal, but after killing Lord Blackwood and wounding Jarod, he was sentenced to life imprisonment by the arriving Malfurion.
The idea of detonating the Well of Eternity and blasting the Burning Legion back home had clearly been something he and his brother devised together. He had merely carried it out, yet he had to bear a whole list of charges: destroying the well water, murdering The Queen, colluding with demons, harming his people, destroying the environment, and more.
But what could Illidan say in the face of those accusations? Explain to everyone that Malfurion and Tyrande had been participants too?
Looking at the Tyrande he loved, he knew that she loved Malfurion. To keep her from grieving, Illidan shouldered every crime alone and was thrown into the underground prison, where he had remained ever since.
Even then, Maiev Shadowsong thought Malfurion had not been fair enough. In her view, only executing Illidan would count as justice. After even Jarod himself rejected that idea, she settled for the next best thing and volunteered to guard Illidan personally.
That way, if Illidan ever tried to escape, Maiev would have every justification to kill him.
He had seen humans before, but the other