 There's still no known motive for the shooting carried out by Thomas Crooks in Butler, Pennsylvania, but ABC Chief Justice correspondent Pierre Thomas says we do know a little more about the minutes leading up to it. Butler town officials confirming that after they became aware of the threat, a local police officer climbed up to the roof and confronted Crooks, but did not succeed in stopping him. Investigators now trying to determine whether roof access had been properly locked down. The shooter climbing up seemingly unimpeded.