Match Point

Chris Wilton, a recently retired tennis professional, is taken on as an instructor at an upmarket club in London. He strikes up a friendship with a wealthy pupil, Tom Hewett, after discovering their common affinity for opera. Tom's older sister, Chloe, is smitten with Chris and the two begin dating. During a family gathering, Chris meets Tom's American fiancÃ©e, Nola Rice, and they are instantly attracted to each other. Tom's mother, Eleanor, does not approve of her son's relationship with Nola, a struggling actress, which is a source of tension in the family. Chloe encourages her father, Alec, to give Chris a job as an executive in one of his companies; he begins to be accepted into the family and marriage is discussed.
During a storm, after having her choice of profession attacked by Eleanor, Nola leaves the house to be alone. Chris follows Nola outside and confesses his feelings for her, and they passionately have sex in a wheat-field. Feeling guilty, Nola treats this as an accident; Chris, however, wants an ongoing clandestine relationship. Chris and Chloe marry, but Tom ends his relationship with Nola.
Chloe, to her distress, does not become pregnant immediately. Chris vainly tries to track down Nola, but meets her by chance some time later at the Tate Modern. He discreetly asks for her number and they begin an affair. While Chris is spending time with his wife's family, Nola calls to inform him that she is pregnant. Panicked, Chris asks her to get an abortion, but she refuses, saying that she wants to raise the child with him. Chris becomes distant from Chloe, who suspects he is having an affair, which he denies. Nola urges Chris to divorce his wife, and he feels trapped and finds himself lying to Chloe as well as to Nola. Nola confronts him at his work and he just barely escapes public detection.
Soon after, Chris takes a shotgun from his father-in-law's home and carries it to his office in a tennis bag. On leaving, he calls Nola on her mobile to tell her he has good news for her. He goes to Nola's building and gains entry into the apartment of her neighbor, Mrs. Eastby. He shoots and kills her, then stages a burglary by ransacking the room and stealing some jewelry and drugs. As Nola returns he shoots her in the stairwell. He then takes a taxi to the theater to watch a musical with Chloe. Scotland Yard investigates the crime and concludes it was committed by a drug addict stealing money. The following day, the murder is in the news. Chris returns the shotgun and he and Chloe announce that she is pregnant with Chris's child.
Detective Mike Banner invites Chris for an interview in relation to the murder. Beforehand, Chris throws Mrs. Eastby's jewelry and drugs into the river, but by chance her ring bounces on the railing and falls to the pavement. At the police station, Chris lies about his relationship with Nola, but Banner surprises him with her diary, in which he is featured extensively. He confesses his affair to Banner but denies any link to the murder, and appeals to the detectives not to involve him any more in their investigation, as news of the affair may well end his marriage just as he and his wife are expecting a baby.
Later one night, Chris sees apparitions of Nola and Mrs. Eastby, who tell him to be ready for the consequences of his actions. He replies that his crimes, though wrong, had been "necessary", and that he is able to suppress his guilt. At the same time, Banner dreams that Chris committed the murders. His theory is discredited by his partner, Dowd, who informs him that a drug peddler found murdered on the streets had Mrs. Eastby's ring in his pocket. Banner and Dowd consider the case closed and abandon any further investigation. The film ends with Chloe giving birth to a baby boy named Terrence, and his uncle blessing him not with greatness, but luck, which his father (Chris) has in spades, since he was able to avoid being punished for his crimes.

Question: What does Banner surprise Chris with?
Answer: diary