context: Phillip Colbert, a wealthy industrialist from Chicago is constructing a factory in Sparta, Mississippi. One night, when driving back into town (after a meeting in the plantation home of one of Sparta's leading citizens, a Mr. Arthur Endicott), to the hotel where he and his wife are staying during the plant's construction; he's murdered. His body is found on the pavement at the front of an alley's entrance onto, Sparta's Main Street. Sparta Policeman Sam Wood discovers the body, during his motor patrol of Sparta, on the second-half of the first shift (11:00 p.m. 7:00 a.m.), about 3:30 a.m. White police Chief Bill Gillespie (Rod Steiger) arrives on the scene where the body has been discovered and begins by taking direct charge of the investigation. A local undertaker and free-lance photographer, have been summoned to the scene to assist the police; to take photographs, and do their best to support the beginning of the investigation. The undertaker tells Gillespie (crucially incorrectly), that it is his immediate guesstimate, that the death has occurred no more than a couple of hours earlier, than the time of the body's discovery by Wood, between say, 12:30 and 01:30 a.m. Gillespie is also told by Wood that his patrol; overall has been quiet, without incident, and with no one seen ("I mean not even a cat", is his quote). But Gillespie, speculating that the crime may have been committed by a transient (and having been wrongly advised of the probable time of death; as being no more than a couple of hours earlier), orders Wood to go back on his patrol and verify that the pool hall is closed (its hours had it open until 12:30 a.m.); the streets and alleyways are clear; and that the train and bus depots, are cleared as well.
  Officer Wood in rechecking the train depot (where the ticket, freight, and baggage offices are all closed, and the station is unmanned); finds (in the still open waiting room), an African-American northerner Virgil Tibbs (Sidney Poitier), sitting quietly with his luggage, and in a business suit (at little after 4:00 a.m. in the morning), waiting upon; what clearly seems to be, no train. Officer Wood immediately arrests him (at gunpoint), cursorily searches him; and finds more than $100 in cash in his wallet. So he takes him in to the Sparta police HQs, where he presents him to the Chief of Police, as a just apprehended murder suspect. Gillespie, prejudiced against blacks, jumps to the conclusion that he has his culprit (attempting to "flee" Sparta, via a train depot that is closed). But he's embarrassed to learn that Wood has arrested a Police Lieutenant; who, in addition to having over $100 in his wallet, also had his official badge of an Officer, not a patrolman; and, his Philadelphia, Police Department photo identification.
  Tibbs , an experienced Philadelphia homicide detective was simply passing through Sparta's depot, on a "blind transfer" - change-in-trains at Sparta from Philadelphia (Mississippi), where he was visiting his mother. After the racist treatment that he receives, Tibbs wants nothing more than to leave as quickly as possible, but his own chief, after questioning whether Tibbs himself is prejudiced, has him stay and help. Leslie Colbert (Lee Grant), the victim's widow, already frustrated by the ineptitude of the local police, is impressed by Tibbs's expertise when he clears another wrongly accused suspect whom Gillespie has arrested on circumstantial evidence. She threatens to stop construction on the much needed factory unless Tibbs leads the investigation. Unwilling to accept help, but under orders from the town's mayor, Gillespie talks a reluctant Tibbs into working on the case.
  Despite the rocky start to their relationship, the two policemen are compelled to respect each other as they are forced to work together to solve the crime. Tibbs initially suspects wealthy plantation owner Eric Endicott (Larry Gates), a racist who publicly opposed the new factory. When he attempts to interrogate Endicott about Colbert, Endicott slaps him in the face; but Tibbs slaps him back, which leads to Endicott sending a gang of hooligans after Tibbs. Gillespie rescues him from the fight and orders him to leave town for his own safety, but Tibbs has caught the "scent"; he's on the trail of a murderer; and he's convinced he'll solve the case. So he refuses to leave until he has solved it.
  Tibbs' examination of Colbert's body has already placed the murder much earlier in the night, than either Gillespie or the Sparta police had initially thought. He's examined Colbert's car, and knows that it was used to drive the dead man's body back, from an as yet unknown location; where, Colbert was actually killed; and, driven back into Sparta, where his body was dumped at an alley's entrance to Main Street.
  So he asks Sergeant Sam Wood (Warren Oates); who discovered the body, to retrace his movements during his patrol shift, on the night of the murder. Tibbs knows that an earlier time of death for Colbert means; that Colbert was murdered, and his body driven around Sparta; and dumped into an alley, all the while Woods was on patrol. that Tibbs and Gillespie accompany Wood on his patrol route, stopping at a diner where the counterman, Ralph Henshaw (Anthony James), refuses to serve Tibbs. When Tibbs notices that Wood has deliberately changed his route, Gillespie starts suspecting Wood of the crime. Tibbs indicates that he knows why Sam has changed his route but will not disclose the reason to Gillespie. When Gillespie discovers that Wood made a sizable deposit into his bank account the day after the murder (which Wood claims is gambling winnings) and Lloyd Purdy (James Patterson), a local, files charges against Wood for getting his 16-year-old sister Delores (Quentin Dean) pregnant, Gillespie arrests Wood for the murder, despite Tibbs's protests. Purdy is insulted that Tibbs, a black man, was present for his sister's interrogation about her sexual encounter with Wood, and he gathers a mob to get his revenge on Tibbs.
  Tibbs is able to clear Wood by finding the original murder scene and pointing out that Sam would not have been able to drive two cars at the same time, his police patrol car and the victim's car. Tibbs also admits that he knew immediately that Wood changed his route not to hide the fact that he was a murderer, but was a peeping Tom, and declined to publicly reveal this in order to spare Wood embarrassment.
  Acting on a hunch, Tibbs tracks down the local back-room abortionist, who reveals that someone has paid for Delores to have an abortion. When Delores arrives, Tibbs pursues her outside, where he is confronted by the murderer, Henshaw. Purdy's mob tracks down Tibbs at this moment, and he is being held at gunpoint when he proves to Purdy that it was Henshaw, not Wood, who got Delores pregnant, and Henshaw shoots Purdy dead before being disarmed by Tibbs. Henshaw is arrested and confesses to the murder of Colbert. He had robbed Colbert to gain money to pay for Delores's abortion, but had killed him in the process.
  His job done, Tibbs finally boards the Gulf, Mobile &amp; Ohio train out of town, after being bid farewell by a now respectful Gillespie.
question: Who slaps Tibbs in the face?
answer: Endicott