question:  Why do the gangs pick Halloween night to fight?
context: Hoodlums fear his fury—and, for that matter, so do the cops! There was Charlie Casale, getting ten dollars dimes, six dollars nickels and four dollars pennies for his father in the grocery store down the street. The three bank robbers looked like triplets. From the ground up, they all wore scuffy black shoes, baggy-kneed and unpressed khaki trousers, brown cracked-leather jackets over flannel shirts, white handkerchiefs over the lower half of their faces and gray-and-white check caps pulled low over their eyes. One of the others took the pistol away from Mister Anderson, the guard, and said to him in a low voice, "Think about retirement, my friend." The third one, who carried a black satchel like a doctor's bag, walked quickly around behind the teller's counter and started filling it with money. The man who had first spoken herded the tellers, Mr. Featherhall and the customers all over against the back wall, while the second man stayed next to Mr. Anderson and the door. She fell unconscious to the floor, and all three of them ran out of the bank to the car out front, in which sat a very nervous-looking fourth man, gunning the engine. Two police cars came driving down the block and a half from the precinct house to the bank, and the car with the four robbers in it lurched away from the curb and drove straight down the street toward the police station. The police cars and the getaway car passed one another, with everybody shooting like the ships in pirate movies. There was so much confusion that it looked as though the bank robbers were going to get away after all. Except that in the trunk lid the owner had burned in 'The Scorpion' in big black letters you could see half a block away." "If I'm making just a quick stop—I never spend more than five minutes with any one customer—I always leave the keys in the car. "It was four professional criminals, I thought you knew that.
output:  The cops would be preoccupied with other matters, and it was easy to explain why you had a weapon on you.
options:  The schoolyard would be empty as kids would be out.  They could be out past curfew without suspicion. No one would question why kids were going out on Halloween night.  The cops would be preoccupied with other matters, and it was easy to explain why you had a weapon on you.  The cops wouldn't be on lookout on a night like Halloween, so they can get away with doing what they want.