  We reinvestigate the emission of Hawking radiation during gravitational
collapse to a black hole. Both CGHS collapse of a shock wave in
(1+1)-dimensional dilaton gravity and Schwarzschild collapse of a spherically
symmetric thin shell in (3+1)-dimensional gravity are considered. Studying the
dynamics of in-vacuum polarization, we find that a multi-parametric family of
out-vacua exists. Initial conditions for the collapse lead dynamically to
different vacua from this family as the final state. Therefore, the form of the
out-vacuum encodes memory about the initial quantum state of the system. While
most out-vacua feature a non-thermal Hawking flux and are expected to decay
quickly, there also exists a thermal vacuum state. Collectively, these
observations suggest an interesting possible resolution of the information loss
paradox.
