I guess it really doesn't matter if you ignore the fact that the radar can only "track" transponders and therefore, if it was "tracking" something real, whatever it was, was squawking an IFF code. I'm not terrorist, but if I ever planned on trying to take out a commercial airliner, I wouldn't squawk an IFF code announcing my presence to every aircraft within 100 miles that had a TCAS system on board (and that would be every commercial aircraft within 100 miles). Furthermore, since the only track the "radar" can see is an IFF track, if the "target" really got that close to AA 612, it would have set off a TCAS alert AA 612 that would be recorded and traceable.