  Suppose an unpredictable evader is free to move around in a polygonal
environment of arbitrary complexity that is under full camera surveillance. How
many pursuers, each with the same maximum speed as the evader, are necessary
and sufficient to guarantee a successful capture of the evader? The pursuers
always know the evader's current position through the camera network, but need
to physically reach the evader to capture it. We allow the evader the knowledge
of the current positions of all the pursuers as well---this accords with the
standard worst-case analysis model, but also models a practical situation where
the evader has "hacked" into the surveillance system.
  Our main result is to prove that three pursuers are always sufficient and
sometimes necessary to capture the evader. The bound is independent of the
number of vertices or holes in the polygonal environment. The result should be
contrasted with the incomplete information pursuit-evasion where at least
{\Omega}(\surd h + log n) pursuers are required just for detecting the evader
in an environment with n vertices and h holes.
