  In the information loss problem in black hole evaporation, investigation of
the purification partner of a Hawking particle is crucial. It is a well-known
fact that 3+1 dimensional spherically symmetric gravitational collapse can be
approximately described by 1+1 dimensional moving mirror models. Since a
detected particle in field theory is defined by what a particle detector
observes, the diversity of detector designs yields a variety of particles and
their partners. We provide a formula of generalized partners of detected
particles emitted out of mirrors in arbitrary motion in a free massless scalar
field theory. Using the formula, we directly demonstrate information storage
about pre-thermal information in a pure state of a Hawking particle and its
partner. The partner form drastically changes depending on the detailed designs
of particle detectors for the Hawking radiation. In a case of the Hawking
particle and its partner sensitive to information about pre-thermal era,
spatial configurations of the partner has long tails in a stage where only
zero-point fluctuation is emitted out of the mirror.
