This will change bigtime, come January 1 2020, when ADS-B "out" is required equipment. The new transponder capability will transmit the aircraft call sign continuously. I suppose one could try to evade by shutting it off, but that in of itself gets one in a heap o' trouble. And, in this case, it was probably just a wayward lost pilot. Actually, this plane may already have ADS-B "out", and the identity is already known by the FAA, if not the media.
Must have been Menendez returning from a weekend retreat in the Caribbean.