In "Fahrenheit 451", when and how does Beatty find out that Montag possesses books and how does he react?

Late in the first section of the book, the day that Montag stays home from work sick, Beatty comes to see him.  He knows then that Montag has books.  He comments to Montag, "At least once in his career, every fireman gets an itch."  He is referring to books.  He says that they (the government presumably) understand this "itch" and they allow a fireman to keep the book for a day, then burn it without penalty.  After that, Beatty seems to fully recognize the fact that Montag has books and that Montag is turning his allegiance away from the government and toward the secret society of books.  Beatty doesn't do anything to Montag right away because he hopes that Montag will turn in the books on his own.  When that doesn't happen and Mildren turns in Montag, Beatty is there to taunt Montag as the firemen prepare to burn Montag's house.  Beatty taunts Montag to the point that Montag burns him and then Montag realizes that Beatty wanted to die.