  We investigate the causal structure of the Harada-Iguchi-Nakao (HIN)'s exact
solution in detail, which describes the dynamical formation of naked
singularity in the collapse of a regular spherical cluster of counterrotating
particles. There are three kinds of radial null geodesics in the HIN spacetime.
One is the regular null geodesics and the other two are the null geodesics
which terminate at the singularity. The central massless singularity is
timelike naked singularity and satisfies the strong curvature condition along
the null geodesics except for the instant of singularity formation. The cluster
dynamically asymptotes to the singular static Einstein cluster in which
centrifugal force is balanced with gravity. The HIN solution provides an
interesting example which demonstrates that collisionless particles invoke
timelike naked singularity.

General Relativity and Quantum Cosmology