  We take a null hypersurface (the causal horizon) generated by a congruence of
null geodesics as the boundary of the Doran-Lobo-Crawford spacetime, to be the
place where the Brown-York quasilocal energy is located. The components of the
outer and inner stress tensors are computed and shown to depend on time and on
the impact parameter $b$ of the test particle trajectory. The surface energy
density $\sigma$ on the boundary is given by the same expression as that
obtained previously for the energy stored on a Rindler horizon.
