I think what Kaitak was getting at when he mentioned that the plane was circling, is that when the 737 is configured for approach with flaps at 1, with weights greater than 110,000 lbs, and flying slow below 190 knts, below what they call the crossover speed, its ailerons do not produce enough lateral force to counteract the sideslip-induced roll produced as a result of an uncommanded full rudder deflection, should it occur. This is why some airlines, such as USAir, have instructed their pilots to come in faster than normal, to minimize the time spent in this vulnerable part of the flight envelope.
ALPA report on USAir427
We can begin to speculate as to the cause as soon as we know the nature of the crash. If we find out that it hit a mountain, flying too low, then we can forget about the rudder. If, however, it went nose first from 6,000 feet, for no apparent reason in clear weather, then we know that the serial killer has struck again.