"The Dead Ringers"
Batman and Robin arrest Harry and turn him over to Commissioner Gordon for interrogation. But before they can crack him, he's rescued by sleazy lawyer Alfred Slye. Batman deduces that Chandell plans to marry Aunt Harriet and then bump off him and Dick, leaving him as sole heir to the Wayne fortune. But Harry doesn't want Chandell to give up crime, so Harry kidnaps Harriet and holds her for ransom instead.
Gordon and O'Hara interrogate Harry, but when his lawyer shows up the Commissioner suggests they use more subtle techniques. They then turn on the 'Subtle Interrogation Lamp'.
Brains and brawn can only take you so far...