Robert De Niro researched his latest role

”I wanna know what you know.” So said Robert De Niro upon meeting Gavin de Becker, high-profile expert on violent stalkers, psychotic snipers, and every other kind of fixation-prone criminal. As de Becker discovered, De Niro meant his pronouncement literally. The actor was so intent on making the celebrity terrorist he plays in The Fan accurate, he out-obsessed the obsessives he studied.

De Becker’s 46-member L.A. firm, Gavin de Becker, Inc., maintains a vast storehouse culled from thousands of police cases involving the behavioral aberrations of such folks as Robert Bardo (who murdered actress Rebecca Schaeffer) to Tina Marie Ledbetter (she showered Michael J. Fox with 6,000 written death threats). De Niro read case files. He watched taped interrogations. He met with knife salesmen, since that’s what his character hawks. He mastered complex databases used to predict violent behavior. ”By the time he finished,” says de Becker, ”he was competent to come to work for me.” And what insights did Bobby glean? ”He grasped that stalkers aren’t starstruck or shy, they’re grandiose. They feel they deserve fame.”

Of course, such pregame prep isn’t unusual for De Niro. ”He’s a brilliant reporter,” says author Nicholas Pileggi, who watched the actor soak up Mob culture — and couture — while working together on GoodFellas and Casino. De Niro’s most flabbergasting fact-finding foray? Shopping for 24 silk shirts with real-life capo Frank Rosenthal. When this performer plays ball, you’d better believe he gets the uniform down — right to the last button.