Looking back what happened in those days, there were lots of events assumed to be a CIA confirmation.
For example, I was shouted by the man in the elevator who said that it was our fault that the Sep 11 attack took place. At that time, I did not realize that he said this to me and just assumed it was said to others around me.
One of my colleagues was a Sikh wearing a turban around the head, which looked like a Taliban, but as a matter of fact, he was even not a believer of the Islam.
The US can confirm this authenticity as I had been on the CIA watch list since born and flagged as a terrorist suspect related to the Sep 11 attack. In this specific occasion, this man clearly mentioned the Sep 11 attack, though I had no idea it was told to me. If I knew it was the word toward me, they could have confirmed that I was one of the terrorist suspects, and when not, they should have noticed I was not one of them.
This is one of the methodologies of the spy as they do not require a concrete information as they do not run a crime investigation to prosecute the subject later on. They just need a confirmation in a different way, and at the same time, they could hide a trace of the intelligence operation in this way without a direct interrogation. That is one of the reasons why I had not realized I was targeted by the spy for a long time.
There were other operations they left a proof, one of which was that I was called at an airport when I was on the cue, and they took me to the different place to open my luggage.
I was the only person taken out in the line and thought it was a racial discrimination, but I did not protest it as it happened in December 2001 at the JFK airport in New York.
This was actually a result of their suspect that I was related to the Sep 11 attack. It made sense to check all of my belongings, but I had no idea I was a suspect or even flagged as a terrorist as I was falsely condemned as the left extremist meeting with the infamous terrorists.
The point here was that the CIA or FBI asked an airport security to confirm my belongings, which should have left a proof that I was a suspect out of the CIA control. This fact also proved that I was framed as a terrorist related to Sep 11 attack by officers who really knew the attack beforehand.