Later in the day, Tom reports back to Jeff with witness accounts that rebuff all of Jeff's speculations. The building superintendent and two tenants saw Thorwald leave the apartment with his wife the previous morning at about 6 am (while Jeff was sleeping) to go to the railroad station. Thorwald allegedly put her on a train to the country. Jeff doesn't believe that anyone actually saw her get on the train: "Well, what good's his information? It's a second-hand version of an unsupported story by the murderer himself, Thorwald." To counter Jeff's persistence, Tom replies: "Now, did anyone, including you, actually see her murdered?"

"Solving the case" rather than appearing "foolish," Jeff demands that Tom go over to Thorwald's apartment for a search before the evidence disappears: "It must be knee-deep in evidence." Tom refuses capitulating to his "amateur sleuth" friend, citing proper judicial procedures and the Constitution's Bill of Rights. He must follow the legal requirements for a judge-issued search warrant (based upon substantial evidence). Jeff becomes passionately sarcastic and critical of his cool and professional detective/friend:

Jeff: What do you need? Bloody footsteps leading up to the door?
Tom: One thing I don't need is heckling.

As Tom prepares to leave, he matter-of-factly informs Jeff of one further finding - the retrieval of a postcard in Thorwald's mailbox from his wife Anna (mailed the previous day at 3:30 in the afternoon). It says that she arrived safely in Meritsville, 80 miles to the north. The postcard's message: "Arrived OK. Already feeling better. Love, Anna." Once he is left alone, Jeff seems disappointed by the news. He extends his reach with the back scratcher to relieve the itch on his big toe.

That night, Jeff observes more activities of his neighbors with the aid of his camera's telephoto lens. Thorwald's actions raise further suspicions in his mind:

• The dog is lowered in the basket to the salesman's garden.
• 'Miss Lonelyhearts' primps in front of her dressing room mirror, takes a few stiff drinks and then goes out, apparently looking for male company.
• The composer entertains well-dressed female guests in his studio.
• 'Miss Torso' rehearses a dance with a male partner and a female choreographer.
• 'Miss Lonelyhearts' enters a restaurant across the street and is seated alone at a table. The view is accompanied by a song with appropriate lyrics: "Many dreams ago, I dreamed many dreams waiting for my true love to appear though each night.." - she also briefly speaks to a passing Thorwald.
• Thorwald arrives home carrying a "EAGLE HEAD" laundry box from the cleaner's, enters his apartment, takes the shirts out of the laundry box and begins packing a suitcase. (Worried that Thorwald is leaving, Jeff frantically calls Tom to come over, and then leaves a message for him.)
• Thorwald talks on the phone in the living room while sifting and rummaging through the contents of his wife's alligator handbag - he handles her rings and jewelry. He lingers on a gold-banded (wedding?) ring. [The woman's purse and jewelry is a Freudian reference to female sexuality.]
• More guests arrive - Village intellectuals - at a noisy party in progress in the musician's studio.

Lisa, wearing a new hat and outfit, enters Jeff's darkened apartment finding him peering out the window. After being briefed by Jeff on Thorwald's latest behaviors ("He's getting ready to pull out for good..."), Lisa explains how she has had a difficult time keeping focused on her work, because her mind has been focused on the mystery. She questions why Mrs. Thorwald would unpredictably leave behind her "favorite handbag" (with jewelry) hanging from her bedpost:

Lisa: It doesn't make sense to me...Women aren't that unpredictable...A woman has a favorite handbag and it always hangs on her bedpost where she can get at it easily. And then all of a sudden, she goes away on a trip and leaves it behind. Why?
Jeff: Because she didn't know she was going on a trip. And where she's going she wouldn't need the handbag.
Lisa: Yes, but only her husband would know that. And that jewelry. Women don't keep their jewelry in a purse, getting all twisted and scratched and tangled up.
Jeff: Well, do they hide it in their husbands' clothes?
Lisa: They do not. And they don't leave it behind either. Why, a woman going anywhere but the hospital would always take makeup, perfume, and jewelry...That's basic equipment. And you don't leave it behind in your husband's drawer in your favorite handbag.

Then, she speculates that Thorwald is involved in an adulterous relationship with a female accomplice in the murder of his wife. Jeff is pleased with her deductive reasoning and hypothesis, and for once erotically attracted to her now that she has begun to take his views seriously:

Lisa:...That couldn't have been Mrs. Thorwald...or I don't know women.
Jeff: Well, what about the witnesses?
Lisa: We'll agree they saw a woman but she was not Mrs. Thorwald, that is, not yet.
Jeff: Is that so? Come here... (She sits on his lap and kisses him.)

While they kiss and talk, Lisa boldly announces that she intends to spend the night with him, to strengthen the potential come-back of their love affair:

Lisa: We have all night...I'm going to stay with you.
Jeff: Well, you'll have to clear that with my landlord.
Lisa: I have the whole weekend off.
Jeff: Well, that's very nice, but I just have one bed.
Lisa: If you say anything else, I'll stay tomorrow night, too.
Jeff: I won't be able to give you any pajamas.

To prove that she can travel light, if necessary, and "live out of one suitcase," she proudly displays her one handbag-sized trick black "suitcase," filled with frilly, pink, overnight lingerie and slippers. With lines dripping of sexual double entendre, Lisa meets his challenge of going on an adventure when she offers him an unbelievable trade - her "feminine intuition" for a "bed for the night":

Lisa: You said I'll have to live out of one suitcase. I'll bet yours isn't this small?
Jeff: This is a suitcase?
Lisa: Well, a Mark Cross overnight case anyway. Compact, but, uh, ample enough. (She pulls her frilly lingerie from inside.)
Jeff: Looks like you packed in a hurry. Look at this. Isn't that amazing?
Lisa: I'll trade you. My feminine intuition for a bed for the night.
Jeff: I'll go along with that.

She is drawn to listening to the melodious sound of the composer's piano playing ("Mona Lisa") in the apartment across the way during his party, asking:

Lisa: Where does a man get inspiration to write a song like that?...(Lisa reclines on the couch by the window.) It's utterly beautiful. Wish I could be creative.
Jeff (teasing): Oh sweetie, you are. You have a great talent for creating difficult situations.
Lisa: I do?
Jeff: Sure. Staying here all night, uninvited.
Lisa: Surprise is the most important element of attack. And besides, you're not up on your private eye literature. When they're in trouble, it's always their Girl Friday who gets them out of it.
Jeff: Well, is she the girl that saves him from the clutches of the seductive showgirls and the overpassionate daughters of the rich?
Lisa: The same.
Jeff: That's the one, huh? It's funny, he never ends up marrying her, does he, huh? That's strange.
Lisa: Weird. (She takes off her outer jacket.) Why don't I slip into something more comfortable?
Jeff: By all means.
Lisa: I mean, like the kitchen and make us some coffee.
Jeff: Oh, with some brandy too, huh?

For the second time, the newlywed bridegroom (in his underwear) opens the shade, leans out and puffs on a cigarette. Again, his wife calls him back: "Harry." Tom arrives and notices Lisa's nightgown in her open suitcase [often glancing at it like it is incriminating evidence] and the now-boisterous party in the composer's studio. Lisa's first words to Detective Doyle, after an introduction, are: "We think Thorwald's guilty." Tom knowingly glances once more at Lisa's suitcase, and Jeff cautions: "Careful, Tom." [His caution of making rash judgments and jumping to conclusions is, of course, a warning that Jefferies needs to heed himself.]

Lisa has become convinced of the truth of Thorwald's guilt - Thorwald must have murdered his wife because, according to her, no woman goes on a trip leaving behind her favorite jewelry (or handbag). After being told their suspicions and Lisa's "feminine intuitions" about the handbag and jewelry, detective friend Doyle concludes that Lars has not murdered and dismembered his wife after having checked out the wife's whereabouts:

Tom: (in close-up) Lars Thorwald is no more a murderer than I am.
Jeff: You mean to say you can explain everything that's gone on over there and is still going on?
Tom: No, and neither can you. That's a secret, private world you're looking into out there. People do a lot of things in private that they couldn't possibly explain in public.
Lisa: Like disposing of their wives.
Tom: Get that idea out of your mind. It will only lead in the wrong direction.
Jeff: What about the knife and the saw?
Tom: Did you ever own a saw?
Jeff: At home in the garage, I had...
Tom: How many people did you cut up with it? Or with the couple of hundred knives you probably owned in your life? Your logic is backward.
Lisa: You can't ignore the wife disappearing and the trunk and the jewelry.
Tom: I checked the railroad station. He bought a ticket. Ten minutes later, he put his wife on the train. Destination? Meritsville. The witnesses are that deep.
Lisa: That might have been a woman, but it couldn't have been Mrs. Thorwald. That jewelry...
Tom: Look, Miss Fremont. That uh, feminine intuition stuff sells magazines but in real life, it's still a fairy tale. I don't know how many wasted years I've spent tracking down leads based on female intuition....

Before leaving, Tom discusses with them that Thorwald's trunk has been found, tied up because the lock was broken. All it contained was Mrs. Thorwald's clothes, clean and well-packed. Taking everything with her, Tom suggests it could be because there is a "family problem" and she isn't planning on coming back. Jeff asks why Thorwald didn't tell his landlord that she wasn't coming back, speculating that he was hiding something. Doyle looks at Lisa's suitcase and its provocative nightgown and asks pointedly:

Tom: Do you tell your landlord everything?
Jeff: I told you to be careful, Tom.
Tom: If I'd have been careful piloting that reconnaissance plane during the war, you wouldn't have had the chance to take the pictures that won you a medal and a good job and fame and money.

Tom then takes a long glance at Lisa, as if to add her to Jeff's list of accomplishments and prizes. After Lisa asks if Tom is "through with the case," he confirms that there isn't enough evidence to support a murder theory: "There is no case to be through with, Miss Fremont." Lisa crosses over to Jeff's wheelchair, symbolically signifying her support of her fiancee. Realizing that she is siding with Jeff and their socializing isn't going as planned, Tom delivers a curt "exit line": "Oh Jeff, if you need any more help, consult the yellow pages in your telephone directory." His final bit of news is that the trunk was delivered to Mrs. Anna Thorwald. Its delivery was recently confirmed in Meritsville - Lars' wife signed the delivery note for the trunk.

After coldly disagreeing with them, Doyle leaves, with ironic parting words: "Don't stay up too late." Jeff and Lisa are dejected, and turn once again toward their neighbors' activities:

• The drunken party guests at the composer's place sing "Mona Lisa."
• 'Miss Torso' exercises her legs while lying on her bed.
• 'Miss Lonelyhearts' brings home a male guest. When the guest aggressively kisses her, she lowers her blinds for privacy. After he forces her down on the couch and sexually assaults her, she angrily slaps him and dismisses him from her apartment, and then goes back to her couch and collapses, crying. [The words of the song 'Mona Lisa' signify her victimization by male violence.]

After witnessing the despairing 'Miss Lonelyhearts,' both Lisa and Jeff wonder whether they are becoming too involved in the lives of others. They doubt the morality of their own probings and convictions:

Jeff (thoughtfully): You know, much as I hate to give Thomas J. Doyle too much credit, he might have gotten ahold of something when he said that was pretty private stuff going on out there. I wonder if it is ethical to watch a man with binoculars and a long-focus lens. Do you, do you suppose it's ethical even if you prove that he didn't commit a crime?
Lisa: I'm not much on rear-window ethics.
Jeff: Of course, they can do the same thing to me. Watch me like a bug under a glass if they want to.
Lisa: Jeff, you know if someone came in here, they wouldn't believe what they'd see.
Jeff: What?
Lisa: You and me with long faces, plunged into despair because we find out a man didn't kill his wife. We're two of the most frightening ghouls I've ever known. You'd think we could be a little bit happier that the poor woman is alive and well. (She leans over the back of his wheelchair to kiss him on the neck.) Whatever happened to that old saying: 'Love thy neighbor'?
Jeff: (Laughs) You know, I think I'll start reviving that tomorrow. I'll begin with 'Miss Torso.'
Lisa: Not if I have to move in to an apartment across the way and do the Dance of the Seven Veils every hour. (She lowers the bamboo blinds on the four windows - in preparation.) The show's over for tonight. (She picks up her overnight kit of lingerie and starts into the next room to change for bed.) Preview of coming attractions. Did Mr. Doyle think I stole this case? [Linking her case to the criminal investigation.]
Jeff: No, Lisa, I don't think he did.

After some moments, Lisa emerges in the doorway, enticing him by gracefully floating into the room wearing an elegant white silk nightgown - her "preview of coming attractions" for an intimate evening:

Lisa: What do you think? (Jeff is speechless.) I will rephrase the question.
Jeff: Thank you.
Lisa: Do you like it?
Jeff: Yes, I like it.

Suddenly, a desperate scream in the courtyard shatters the night air. As everyone moves to their apartment windows (and Lisa opens their middle blind), they see the female dog owner crying out from her fire escape - her dead dog lies on the concrete in front of Thorwald's garden - maliciously killed with its neck broken. The strangled dog's body is drawn up on the pulley. The distraught woman sobs piteously in disbelief, crying out and accusing the other anonymous, uncaring apartment dwellers - who appear in separate, individual closeups: "You don't know the meaning of the word 'neighbor'":

Which one of you did it? Which one of you killed my dog? You don't know the meaning of the word 'neighbor.' Neighbors like each other, speak to each other, care if anybody lives or dies, but none of you do. But I couldn't imagine any of you bein' so low that you'd kill a little helpless, friendly dog - the only thing in this whole neighborhood who liked anybody. Did ya kill him because he liked ya? Just because he liked ya?

Jeff notices that the only person who doesn't emerge from inside when the dog is discovered is Thorwald, seen smoking a glowing cigarette in his darkened apartment. Lisa suspects that the little dog was killed "because it knew too much."