So many great and memorable scenes and lines, but still the top choice ultimately HAS to be the one that ultimately punches you in the stomach, knocks the wind out of you, and ultimately leaving you gasping for air...
"the startling and despairing ending scene, the only scene in the film that actually takes place in Chinatown, all the characters converge including the unsuspecting police (on Cross' payroll: "He owns the police").
The sequence opens in the circumscribed area beyond true police and governmental control with passing views of neon-lighted Chinese restaurants and colorful lanterns, accompanied by discordant, blaring piano chords and a snare drum. Gittes notices that his operatives Walsh and Duffy have already been handcuffed. He appears willing to escape from Cross and holds out his hand to be cuffed by Escobar's partner, Loach, "for withholding evidence, extortion, accessory after the fact." But Gittes' protests are ignored when he argues, powerlessly, that Cross, Evelyn's incestuous father, is "the bird you're after...He's crazy, Lou. He killed Mulwray because of the water thing...Lou, you don't know what's going on here, I'm tellin' ya."
During Evelyn's getaway with Curly and the butler and maid in their native town, Cross finally catches up with his two daughters. He stumbles when guiltlessly identifying himself to the girl as her grandfather. Evelyn pushes her evil father away and attempts to get her depraved father away from the girl. Cross pleads with her to release the young girl - his offspring:
Cross: Evelyn, pleeease, pleeease be reasonable...How many years have I got? She's mine too?
Evelyn: She's never going to know that.
With that, Evelyn pulls out a small pistol and threatens her father. Gittes suggests letting the police handle everything, but she replies with futility: "He owns the police." Cross tries to reason with her and accuses her of being neurotic and paranoid: "Evelyn, you're a disturbed woman, you cannot hope to provide...You'll have to kill me first." And with that, she wounds her father in the arm in full view of everyone, and then attempts to escape by car with Katherine.
In the gripping final scene, Escobar fires his pistol twice into the air as a warning, and then once at the car's tires. Loach, still handcuffed to Gittes, takes three more shots at the escaping car as it recedes out of view - and one of his shots is fatal. Suddenly the car slows to a stop in the far distance. The blaring horn of the car signals a death for Jake. [The horn also sounded when Evelyn's head fell forward onto the car's wheel outside the house where Katherine was being kept.] There are Katherine's screams, as the awful, horrible scene is revealed - slumped over the wheel of her car is Evelyn, shot through the head from behind. Gittes is the first to get to the car - he opens the driver's door and she flops to the side. Her face is horribly blown apart through her flawed eye - she has literally been destroyed by her father. Escobar has the cuffs removed from Gittes' arms when he orders: "Turn them all loose." Cross, lamenting "Lord, Oh Lord," clumsily shields and covers the eyes of an hysterical Katherine - telling her "Don't look, don't look" - to prevent her from comprehending the enormous tragedy. The domineering, capitalistic water tycoon and controlling father/grandfather comforts her and ends up taking her away.
Powerless to prevent the inevitable tragedy that he has exposed, Jake is stunned, shocked, and numb -- and cannot help but recognize (and see) the part he played in it. He is filmed in stark profile from the left, accentuating the stitches on his wounded nose. With Jake's last words, he mumbles what he told Evelyn he used to do in Chinatown and has again succeeded in doing: "As little as possible." His meddling into the mystery, and his emotional involvement in this case has led to a chaotic finale, where he is left to repeat past history in the dark streets of Chinatown.
The devastated Gittes is ordered by Escobar to get the hell out of there and go home as a "favor":
What's that? What's that? You want to do your partner a big favor? (To his men) Take him home. Take him home! Just get him the hell out of here. (To Jake) Go home, Jake. (Whispering) I'm doing you a favor.
Gittes' associate Walsh also tells the detective to lay the inexplicable blame on the foreign area and repress the nightmarish tragedy - as he is led away, in a haunting closing line:
Forget it, Jake. It's Chinatown!
Gittes is cautioned to detach himself emotionally from the case - something that he will find impossible to do. [In the sequel, The Two Jakes (1990), an older Jake is preoccupied by his haunted memories of tragic victim Evelyn and the unanswered question of the fate of her daughter Katherine. After learning Katherine's identity during another case in the conclusion of the sequel, he tells/warns her with these words as the film ends: "It [the past] never goes away."]
Sirens sound as Escobar orders the clearing of curious spectators that are gathering on the street:
All right. Come on, clear the area. On the sidewalk. On the sidewalk, get off the street."