Tonight, a "20/20" exclusive, about something that happened this very hour two months ago. And the father of the young killer speaking out only to Barbara Walters. Tonight, she's back on a special assignment. Well, tonight, this is special. A milestone, the first time that a parent of a mass murderer has ever spoken on television. He's doing this to show other parents the warning signs he missed hopefully so that no one has to go through the night that changed his life and so many others, forever. Barbara Walters interviews Peter Rodger. Jennifer Joseph and Muriel Pearson produce the special. Yuval David does voice over, reading from the manifesto of killer Elliot Rodger.