Iran’s FM Abbas Araghchi on elimination of Ali Khamenei:

The enemy were aware these meetings were taking place, and that points to the existence of a security breach -- a breach that has probably still not been completely eliminated and needs to be addressed.

The security services are investigating the matter.

In my opinion, they knew very well that the Supreme Leader is in his office every morning, making that a readily identifiable target.

But they had also realized that a meeting of military commanders was taking place in the adjacent building --or perhaps one or two buildings away--and that is why they chose that particular time to attack.