Did the bridge take a while to fall apart. It didn't happen within a second or so did it? Also didn't it break up into chunks instead of the entire tail falling off the plane? Wouldn't the bolts holding the tail on break first considering they are the weakest point?
It took hours for the oscillations to build up in the bridge to the point of failure. However, flutter is a known and real phenomenon in aerodynamics -- wings and tails have fallen off of a/c, especially on initial test flights, and especially in the 1930s and 40s before the phenomenon was better understood.
Why would it take seconds vice hours for the oscillations to build up to the point of failure? Because the resonant frequencies of a "bridge" and an "a/c tail" are very different, as are the loads required to stimulate them.
Regarding the structural point of failure, I have heard that the bolts holding the tail in place were found still in place on the fuselage. What failed were the fastening points on the tail structure to which the bolts are attached.