I have just looked at the
NTSB report on TWA800.
On page 91, it shows a synopsis of primary radar returns just after the breakup; the cloud of debris is clearly visible.
The
report on EgyptAir 990 that hit the sea in one piece shows on page 36 that also for this flight, primary returns were available nearly until the impact.
So in either case, the primary radar tapes are badly needed. However, an inflight breakup is made less likely by the lack of any observations: an explosion would be well audible and a cloud of debris rather visible to anyone in the area (probably mostly seafarers). And an impact in one piece would have needed to show on at least one seismograph, which it apparently did not (or at least the corresponding spike is not yet found).
I am not yet convinced that this aircraft has crashed.