Well, you've demonstrated that you REALLY don't understand the conversation.
This was in reference to the FIRST WTC bombing, in 1993--not 9/11. And the NYPD just took the phone call. "Al-Qaeda" wasn't on anyone's radar in February, 1993.
BTW, Destro: yes, someone sympathetic to the Serbs could very easily call in to take credit on behalf of the Serbs. There is a reason why various actors engage in terrorism: it frequently works. In the early days after the WTC bombing, before they ran down the VIN, there was rampant speculation as to whodunit--ranging from Puerto Rican terrorists, to Serb/Croat/Bosniak nutballs, leftovers from the Baader-Meinhof gang.