When he kills Captain Beatty, Montag moves against him merely as a dangerous impediment to his action. However, later on, Montag questions his earlier feelings and regrets his actions.
In the third part of Fahrenheit 451, "Burning Bright," Montag realizes that Mildred has turned him in because Beatty arrives and orders Montag to burn his own house. Hurriedly, Montag destroys his hidden books, but when he drops the miniature transmitters provided by professor Faber, Beatty threatens to trace them to their owner. Determined not to allow harm to Faber, Montag turns the flamethrower upon Beatty, ironically reversing Beatty's philosophy of fire's being "antibiotic, aesthetic, practical" upon his captain. Also, Montag destroys the Mechanical Hound with his flamethrower, but only after it injects his leg with anesthesia.
Later, however, Montag regrets his murder of Beatty as he realizes that he acted irrationally against Beatty, perceiving him as representative of the ills of his society. As he flees with a few books that were not burned, Montag acknowledges that Beatty has taunted him, needling him to kill his captain: "Beatty wanted to die." But Montag is distraught because he really did not want anyone to die; he begins to cry as he envisions Beatty engulfed in flames: "He bit at his knuckles. I'm sorry, I'm sorry, oh God, sorry..."