You can only “admit” something if YOU are the one doing it. You can’t “admit” that someone else committed murder or a robbery. The article’s title is misleading at best and outright propaganda at worst.
ad·mit
[ədˈmit]
VERB
confess to be true or to be the case, typically with reluctance:
“the office finally admitted that several prisoners had been injured” · ““I am feeling pretty tired,” Jan admitted” · “I have to admit I was relieved when he left” · “she admitted her terror of physical contact”
It implies that Amnesty is on their side.
They admit to the knowledge of the act, which implies that they had previously been silent about it.