A bomb in the cargo hold would have blown up the fuselage in midair. This did not happen. The fuselage came down in one piece. The tail clearly snapped off, it was not blown off by a bomb. The engines do not appear to have exploded either.
Sabotage is a different possibility altogether - loosening bolts or otherwise damaging the rudder. But the plane came into JFK from Boston earlier Monday morning, so any sabotage would most likely have to have been done at JFK, in broad daylight, with dozens of people running around. I suppose it is possible that the plane was sabotaged in Boston and the perps did not care where the plane would eventually crash.