A numerical method to reconstruct and interpret magnetotail energetic ion (>0.3 MeV) and electron (>0.2 MeV) bursts is presented in this paper. Numerical calculation of particle trajectories for selected times in burst events are used to investigate possible sources and mechanisms of particle energization. Actual observations of burst events supplied the initial conditions for numerically calculated solutions of the Lorentz force equation. A three-dimensional model of the magnetosphere produced by dipole, magnetopause, and magnetotail currents was used (D. B. Beard et al., 1982). Particle trajectories were computed both in the absence of an electric field, and with electric field introduced locally perpendicular to the magnetic field. Several noteworthy results were obtained from the simulation. While the motions of energetic particles near the nominal neutral sheet are complicated and obviously nonadiabatic, they can, nevertheless, generally be divided into two types, parallel and perpendicular. Proton and electron parallel trajectories had most of their trajectory motion parallel to the magnetic field lines and traveled long distances along field lines even to the near-earth region. Perpendicular proton and electron trajectories traveled much shorter distances with much of their trajectory motion perpendicular to the magnetic field, with proton trajectories having significant interaction with the neutral sheet region. Both protons and electrons mirrored adiabatically at short distances above and below the neutral sheet region, while protons showed a nonadiabatic mirroring in the neutral sheet region. Another important result is that the preferential occurrence of earthward energetic proton burst anisotropies in the premidnight sector is explained by the fact that only the premidnight trajectories connect to reasonable source locations. ¿American Geophysical Union 1987