Charles Katz lived in an apartment house on Sunset Boulevard, in Los Angeles. Almost every day, he walked down the street to a bank of three telephone booths, entered one of them, and made a long-distance call. Katz was a handicapper; he was calling his bookie, in Massachusetts. He had been making his living this way for thirty years. To catch him, the F.B.I. placed microphones on top of two of the phone booths and put an “Out of Order” sign on the third.