  It is recently argued that if the Hawking radiation process is unitary, then
a black hole's mass cannot be monotonically decreasing. We examine the time
dependent particle count and negative energy flux in the non-trivial conformal
vacuum via the moving mirror approach. A new, exactly unitary solution is
presented which emits a characteristic above-thermal positive energy burst, a
thermal plateau, and negative energy flux. It is found that the characteristic
positive energy flare and thermal plateau is observed in the particle outflow.
However, the results of time dependent particle production show no overt
indication of negative energy flux. Therefore, a black hole's birth cry is
detectable by asymptotic observers via particle count, whereas its death gasp
is not.
