The dynamics of the three-body dissociative charge exchange of fast (12 keV) H-3(+) and D-3(+) with Cs have been studied using multiparticle translational spectroscopy. The observed partitioning of product momenta was found to be state-specific and yields insights into the nuclear motion during dissociation for the three lowest-lying 2s (2)A(1)', 2p (2)A(2)", and 3p E-2' metastable Rydberg states of H-3 and the 2s (2)A(1)' and 2p (2)A(2)" states for D-3. These results provide direct empirical information on the nonadiabatic couplings that govern the three-body dissociation of the lowest-lying Rydberg states of H-3 and D-3.