The next day, Jeff's nurse Stella and Lisa (in a flower-print dress) watch out Jeff's rear window as Thorwald is seen scrubbing the walls of the bathroom above the tub in his apartment. Stella is convinced of a murder and states what everyone else is thinking - that Thorwald murdered his wife and dismembered her body in the bath-tub:

Stella: Musta splattered alot. Well why not, that's what we're all thinkin'. He killed her in there. He has to clean up those stains before he leaves.
Lisa: Oh Stella, your choice of words.
Stella: Nobody ever invented a polite word for a killin' yet.

Viewing a two-week old Kodak slide photograph of the garden through a viewer, Jeff anticipates what he will discover: "I think I've solved a murder...I think I know why Thorwald killed that dog." He compares the growth of the flowers in the flower bed, noticing that they were taller earlier than they are now (obviously "there's something in there. Those flowers have been taken out and put back in"). He and Lisa suspect that some incriminating item (maybe the knife and saw, or Mrs. Thorwald's ring) was buried there by Thorwald, near where the overcurious dog was found. Stella has her own grotesque theory that ignores the inconclusive burial idea: "My idea is she's scattered all over town, a leg in the East River..." Lisa is disgusted by the thought, but she is brave enough to propose that they wait until it gets a little darker so she can go and dig up the flowerbed - but her idea is promptly rejected by Jeff.

Jeff has another idea - because Thorwald has been hurriedly packing in his apartment to leave, he proposes getting into Thorwald's apartment as soon as possible, to ultimately locate Mrs. Thorwald's body. He wheels himself around and prints a provocative note in large letters: "WHAT HAVE YOU DONE WITH HER?" and places it in an envelope addressed: "LARS THORWALD." Lisa volunteers to be the messenger and stealthily delivers the note under Thorwald's door - she just misses being detected. Jeff uses his telephoto lens to observe the operation from his window. After reading the note and not finding anyone at his door or on the fire escape, Thorwald goes into his back bedroom and hastily finishes his packing. Stella is relieved: "Thank heaven that's over."

While Lisa rushes back to the apartment, Stella asks to use Jeff's telephoto camera: "Mind if I use that portable keyhole?" He permits her, under one condition: "Go ahead as long as you tell me what you're looking at." She notices 'Miss Lonelyhearts' laying out red pills (possibly in preparation for a suicide with an overdose of pills and alcohol), and then picking up a book with a large cross on its cover (a Bible?).

When Lisa breathlessly returns (as Jeff proudly looks on at his hero), she eagerly and excitedly asks:

Lisa: Wasn't that close? Well, what was his reaction? I mean when he looked at the note.
Stella: Well, it wasn't the kind of an expression that would get him a quick loan at the bank.
Lisa: Jeff, the handbag!

They watch Lars look in his wife's handbag and then place it in his suitcase. Both women suspect that Lars has his wife's gold wedding band in the handbag. When Lisa asks if Stella would ever go anywhere without her wedding band, she imagines a grisly scenario: "The only way anybody could get that ring would be to chop off my finger." Stella wishes to go down and find out what's buried in the garden, and Lisa morbidly concurs that she has always wanted to find buried remains: "Why not? I've always wanted to meet Mrs. Thorwald." Jeff is slightly squeamish, although Lisa is not: "If you're squeamish, just don't look." He doesn't want them to end up with the dog's fate.

In a bold scheme to distract Lars and get him out of the apartment for fifteen minutes so that the women can dig in the garden, Jeff makes his first real contact with Thorwald. He phones the salesman, identifies himself as the note's author ("Did you get my note?"), and tells him to meet him at the bar at the Albert Hotel "right away...a little business meeting to settle the estate of your late wife." Thorwald promptly leaves, presumably for the nearby hotel. Jeff tells the women that he will be their lookout. He will signal Thorwald's return with a flash in the window from his camera's flashbulb. In the courtyard, both women climb the steps and garden wall, similar to the path taken by the cat at the opening of the film, and Stella begins to dig with a shovel where the dog used to sniff about. Jeff telephones Tom Doyle and leaves an urgent message with his babysitter. As she digs, Stella gestures that they haven't found anything.

In a suspenseful scene, Lisa makes a bold but potentially reckless decision to enter and search Lars' apartment while he is gone. Her goal is to find the incriminating evidence - the wedding ring - that will prove Jeff's theory. [Note: Lisa actually enters Jeff's fantasy world when all other enticements and threats to get to his heart fail.] In her full-skirted, flowery dress, she climbs up to his apartment via the exterior fire escape and enters through an open window. Jeff pantomimes a protest from his window, but to no avail. In Thorwald's bedroom, she turns the purse upside down, showing him that it's empty - as Jeff views what she's doing through his telephoto lens. Stella returns to Jeff's apartment, telling him Lisa's instructions: "Ring Thorwald's phone the second you see him come back."

Preoccupied with 'Miss Lonelyhearts' who is conducting a suicide attempt on the ground floor due to her failure to find a suitable companion, Stella convinces Jeff to call the police to alert them, and he is distracted from his look-out duties. Lisa starts looking around the apartment for the jewelry. While he dials the police at the 6th Precinct, the suicidal woman pauses for a moment to listen to the composer's music in an adjacent apartment. The large hulking Thorwald unexpectedly returns just as Lisa seems to have found some evidence. She proudly holds up some of Mrs. Thorwald's jewelry in the living room. As she enters the kitchen in his apartment, she hears Thorwald in the hallway and hides as he enters the front door. Jeff helplessly and impotently looks on as Lisa is trapped, gasping and covering his mouth with feminine gestures. Panicked, he frantically tells the police on the phone about a man molesting a woman in Thorwald's apartment (while totally forgetting about 'Miss Lonelyhearts'): "A man is assaulting a woman at 125 West 9th Street, Second Floor at the rear. Make it fast." [The two dramas happening only a floor apart increase the unbearable tension - a depressed 'Miss Lonelyhearts' below, and a trapped Lisa in the wife-murderer's apartment above.]

In the bedroom, Thorwald notices that the handbag has been moved. Lisa is spotted and confronted by Lars - she backs away from him into the living room. She is grabbed by the arm and thrown down, forced to her knees. Thorwald demands the jewelry back and then struggles with her and violently shakes her. Jeff anxiously and helplessly watches in misery as her screams for help can be heard: "Jeff! Jeff!" As she fends him off and they wrestle with each other, Lars turns out the lights. When the police arrive in the apartment's corridor just in time to prevent any serious injury, they question both Lisa and Thorwald.

In a significant scene as she explains her breaking and entering crime, Lisa positions herself with her back to the window between the real criminal and the authorities. To signal that she has found the ring, she points to Thorwald's wife's wedding ring on her own finger that she waves behind her back. Stella watches with binoculars as Jeff views the scene with his telephoto lens.

[Note: Pointing to the wedding ring on her finger, she courageously reveals that she has discovered the crucial evidence - it is also an expression of her symbolic wish and proposal to be married to Jeff. By wearing the ring, she fulfills her own fantasy. And by daringly placing herself in serious danger and causing him masochistic excitement at the same time, she inspires Jeff toward love, commitment, concern, and marriage in multiple ways, as he watches her through his long telephoto lens.]

While Lisa gestures, Lars notices her signals and the wedding ring, and triangulates the view, spotting the mortal threat. He looks up and discovers that Jeff, his tormentor, is watching from the apartment window across the courtyard, looking directly into his telephoto lens. It is the first time he has noticed the voyeuristic spy in the apartment complex - it is a chilling moment in the film as he sees the threatening spectator and knows where he lives.

When Lisa is led away by police, Stella leaves with their available cash (of about $250 dollars) to bail her out of jail, presumably with a charge of first offense burglary. Just then, Tom Doyle calls, not wanting to be bothered by another "mad-killer" tale. Jeff whispers the latest developments: Lisa's arrest after entering Thorwald's apartment and finding the evidence - Mrs. Thorwald's wedding ring; and Thorwald's killing of a dog that was digging around in the garden where something was buried. Jeff also describes his explanations and theories surrounding Thorwald's murder of his wife:

All those trips at night with that metal suitcase. He wasn't taking out his possessions, because his possessions were still up in the apartment...in sections, and I'll tell you something else. All the telephone calls he made were long-distance. All right, now if he called his wife long-distance on the day she left, after she arrived in Meritsville, why did she write a card to him saying that she'd arrived in Meritsville? Why did she do that?

Doyle promises to "run it down," and get Lisa out of jail without the need of bail money. He also assures Jeff about Thorwald: "If that ring checks out, we'll give him an escort."

In the exciting finale when Jeff is left alone in his apartment, he notices that Lars' apartment is dark. When his phone rings again, he doesn't wait to hear who the caller is. He blurts out:

Tom, I think Thorwald's left. I don't...Hello...

The phone clicks off and disconnects. Jeff slowly realizes his error - it was not the detective. He sits helplessly, listening to noises, glancing around warily, wondering if he will potentially be the next victim - a victim of male aggression like Mrs. Thorwald. While he hears footsteps outside his apartment, Jeff wheels himself around to grab his flash equipment and a long box of flashbulbs to protect himself. Then, he positions himself in front of his rear window so that he is darkly silhouetted by it. Eventually, the dark figure of Thorwald slowly opens the door and enters - he guiltily and pitiably asks:

Thorwald: What do you want from me? Your friend, the girl, could have turned me in. Why didn't she? What is it you want? A lot of money? I don't have any money. Say something. Say something. Tell me what you want! Can you get me that ring back?
Jeff: No!
Thorwald: Tell her to bring it back.
Jeff: I can't. The police have it by now.

Jeff has inserted a flashbulb into his camera's flash mechanism. To blind Thorwald momentarily as he menacingly moves forward to attack, on each of the three steps he takes down to reach his victim, Jeff keeps loading new flashbulbs and firing the flash to keep the killer at a distance. Jeff fights him off by flashing or firing his profession's main instrument - his camera and its exploding flash mechanism [orgasmically or erotically?] - once, twice, three times, and then a fourth time. Each whitish-blue flash is followed by a red after-glow filling the entire frame, from Thorwald's dazed perspective.

Seeing Doyle and Lisa entering Thorwald's apartment across the way, Jeff screams out: "Lisa. Doyle." Thorwald struggles with Jeff, trying to strangle him, and then dumps him out of the wheelchair and through the open window. Jeff hangs and dangles from the window ledge three floors above the courtyard as Thorwald tries to push him to his death. Onlookers from the apartments around the courtyard hear the suspenseful fight - now they are the spectators looking over at Jeff's window. Detectives grab Lars from behind at the last minute, but Jeff lets go and falls backward to the ground below. His fall to the courtyard is partially broken by detectives. Reunited, Lisa cradles Jeff's head in her lap as he tells her: "I'm proud of you."

Jeff sarcastically asks Doyle: "You got enough for a search warrant now?" The police yell down that Thorwald has confessed that he distributed his wife's body parts in the East River: "Thorwald's ready to take us on a tour of the East River." With morbid curiosity, Stella whispers a question to Doyle and learns that because the dog was "too inquisitive," Thorwald dug up Mrs. Thorwald's head from the flower bed and moved it to a hat box in his apartment. Asked if she wants to take a look, Stella replies: "No thanks, I don't want any part of it."

[Note: A gruesome double-entendre was about one of Mrs. Thorwald's body parts - her head? - possibly in the hat box, that causes her to do a double-take]

In the epilogue or final scene, the temperature now reads 72 degrees and the heat wave has broken. The camera makes a wide pan one last time around the courtyard [a wide pan both commences and closes the film in a neatly symmetrical pattern of actions] to resolve the lives of the occupants of the complex in the framed windows:

• 'Miss Lonelyhearts' (now no-longer-lonely) visits the composer in his studio, where he plays his new phonograph hit record release for her (the song that was being composed during the entire film). She tells him: "I can't tell you what this music has meant to me." His beautiful music saved her life and prevented her suicide attempt: "Lisa, with your daffodil April face, Lisa, full of starry-eyed laughing grace; Hold me and whisper the sweet words I'm yearning for; Drown me in kisses, Caresses I'm burning for."
• Painters with paint rollers are busy repainting the vacated Thorwald apartment.
• The childless couple who sleep on the fire escape have acquired a new puppy dog to replace their murdered dog. They lower it in their basket.
• 'Miss Torso' opens her door for Stanley, a chubby, spectacled, Army-uniformed soldier boyfriend (or husband?) and true love, returning home and hungry for what's in the refrigerator.
• The sculptress naps in her lawn chair after finishing her "Hunger" sculpture.
• The newlyweds quarrel for the first time - because the bridegroom quit his job. The bride is disaffected and furious, vowing she wouldn't have gotten married if she had known.

Jeff snoozes [in the same position as in the film's opening] with his back toward his rear window, facing inward and presumably having given up his indulgent spying on others. There is a smile on his face. His fate following the cataclysmic discovery of the murder is that he is doomed to repetition - more helpless convalescence and more time sitting at his window with two broken legs in casts (doubly castrated!). But now the camera finds the recklessly-brave, protective hero Lisa at the side of her flawed fiancee. Her legs are on the sofa next to him - he is not alone this time.

The shot pans up her legs, revealing significantly that Lisa is masculinely-dressed in blue jeans/pants and shirt. [She is not in her typical glamorous, high-fashion outfit - rather, she is the one 'wearing the trousers.'] After noticing that he is asleep and not watching her, she casts off her male image by putting down her adventure tale reading material - Beyond the High Himalayas, by William O. Douglas. She assertively substitutes her own preferred reading material - Harper's Bazaar (the "Beauty Issue"). On the soundtrack is the musician's song: "Lisa." The window shades roll down before the superimposed Paramount Studios logo - the audience members were the ultimate voyeurs "spying" on the entire film, before fading to black.

[Note: One thing to note: there were NO end credits in the original film. The DVD restoration appended end credits, as well as the PG-rating that was applied to the film decades later. (There were no film ratings in 1954.)]