Waco's sister died as a collateral damage during a war, years ago. Erol had his own bunker and members of his team and their families, if they could not fight in the war, were set to hide there.
However, for everyone's safety, it had to be closed before the war began. No matter who was trying to get in beyond this point, even Erol himself, cannot be allowed inside.
This was Erol's strict instruction, and he would not monitor it afterwards.
Waco's sister was late to come over, arriving an hour after the war began. It so happened that leaks entered and passed over the area. The girl died right by the bunker's door.
He thought that Waco understood this. But now he realized that he had always kept the blame and anger in his heart.
That said, while his dying too early was regretful because they couldn't get information, Erol wasn't planning on keeping him alive after an interrogation anyway. They were in the middle of nowhere and were not in a position to drag around a prisoner.
