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One thing I think I can gather from the photos is that neither the mounting brackets, nor the pins failed. So the critical question is whether this was some kind of fatigue fracture in a composite matrix, or whether it was a sudden load (or perhaps a modal vibration failure). The force needed to break the rudder off could be guess-estimated if we knew the approximate material properties of the composite rudder panel attachment points (probably close to steel) and their approximate dimensions. Another way to get an estimate, is by noting that the attachment points themselves did not fail (and if we assume a safety factor of say 3?). So, Freepers, figure out the dimensions of the rudder attachment points, and we ought to be able to figure out how large a force blew that thing off.

By the way, knowing the "G's" a rudder was subjected to is not the same as knowing the force it was subjected to. While G's have meaning in respect to a wing with a known load of passengers. it doesn't make a lot of sense for a rudder without knowing the design load of the rudder.

...So the critical question is whether this was some kind of fatigue fracture in a composite matrix, or whether it was a sudden load (or perhaps a modal vibration failure)....

Well said. If the people who did the design, did it right, there should not be a normally encountered sudden load that could cause such a material failure. Most standard kinds of engineering design review catch problems of this kind. If it is a sudden load that ripped appart the composite matrix structure, it is likely that the load was far greater than anticipated under any normal or abnormal situation likely to be encountered. That in itself would suggest some form of terroist interaction. The lack of physical damage on the surfaces further suggests that this is relatively unlikely.

In design errors, fatigue fractures are far more common, due to the relatively unknown number of and magnitude of the cyclic loadings. All things being equal, a fatique failure is more probable. One thing that could have happened is if the tail surfaces were removed and in the replacement of pins scratches or "stress concentration points" were created in the composite material surfaces. This is another way that things could have failed in the way the photos indicate.