Task: Question Generation
Input (English):  John LeTour, a 40-year-old New Yorker, is one of two delivery men for Ann, who supplies an exclusive clientele in the banking and financing sector with drugs. While Ann contemplates switching to the cosmetics business, LeTour, who suffers from insomnia, has lost his perspective in life.
One night LeTour meets his former girlfriend Marianne, who both once shared an intense but destructive relationship due to drug abuse. Although they stopped taking drugs, Marianne refuses his offer for a new start. After spending one night together, she tells him that this was her way of saying good-bye. Unbeknown to her, her mother died at the hospital while she was with LeTour. The next time he meets Marianne, she attacks him, demanding that he gets out of her life once and for all.
Meanwhile, the police start observing LeTour because one of his clients, Tis, is connected to the drug induced death of a young woman. On his next delivery, LeTour witnesses a heavily drugged Marianne in Tis' apartment. Only minutes after his departure, she falls several stories to her death. LeTour gives the police a lead to Marianne's last whereabouts. At the wake, Marianne's sister Randi tells him not to feel guilty for what happened.
When Tis orders a new supply and insists that LeTour delivers it, he senses that Tis wants to dispose of him. Ann accompanies him, but Tis' guards force her to leave the room. In the subsequent shoot-out, LeTour kills Tis and both of his henchmen, but is left critically wounded. He lies down on the hotel bed, showing no anger or pain, only a profound weariness, as police sirens can be heard in the distance.
Ann visits LeTour in jail, who expresses his relief and hopes for a better future. The film hints at the possibility that Ann will wait for him.
Output (English): Why do the police start obsersving LeTour?