Callahan's unorthodox interrogation and torture are very effective - the location of the girl is extracted from the psycho. [And off-screen, Harry searches - without a search warrant - Scorpio's lodgings and seizes the rifle that he used to kill all his weak and innocent victims: the roof-top swimmer, the 10 year-old black boy, and the officer with a padre's disguise.] But Scorpio's next victim of rape, kidnapping (and murder), 14 year-old Ann Mary Deacon, is found dead in the bluish dawning light of the next scene. Her nude corpse (Debralee Scott) is found in the Marin Headlands on the other side of the Golden Gate Bridge [Battery Spencer, Conzelman Road]. She is hauled out from her 'grave' (a hole in the ground), laid on a stretcher, and covered with a blanket.

After the killer is arrested, however, he is released from custody [with no public reaction???] when the District Attorney, William Rothko (Josef Sommer) argues that the fiend's civil rights were abused, and the detective used extra-legal (or illegal) means ("a very unusual piece of police work - really amazing") to capture and coerce a confession from the pathological threat, and to search the suspect's living quarters. To Harry's complete disgust and incensed surprise, he learns that the killer cannot be charged and he was released on a legal technicality (based upon liberal decisions of the Supreme Court such as Miranda v. Escobedo that protect the rights of accused criminals), and that the case against the psychotic would be thrown out of court if brought to trial - even though they have in their possession the murder weapon:

District Attorney: You're lucky I'm not indicting you for assault with intent to commit murder.
Callahan: What?!
District Attorney: Where the hell does it say you've got a right to kick down doors, torture suspects, deny medical attention and legal counsel. Where have you been? Does Escobedo ring a bell? Miranda? I mean, you must have heard of the Fourth Amendment. What I'm saying is, that man had rights.
Callahan: Well, I'm all broken up about that man's rights.
District Attorney: You should be. I've got news for you, Callahan. As soon as he's well enough to leave the hospital, he walks.
Callahan: What are you talking about?
District Attorney: He's free.
Callahan: You mean you're letting him go?
District Attorney: We have to, we can't try him.
Callahan: And why is that?
District Attorney: Because I'm not wasting a half a million dollars of the taxpayer's money on a trial we can't possibly win. The problem is, we don't have any evidence.
Callahan: Evidence? What the hell do you call that? (He gestures toward Scorpio's weapon on a side table.)
District Attorney: I call it nothing, zero.
Callahan: Are you trying to tell me that Ballistics can't match the bullet up to this rifle?
District Attorney: It does not matter what Ballistics can do. This rifle might make a nice souvenir. But it's inadmissible as evidence.
Callahan: And who says that?
District Attorney: It's the law.
Callahan: Well then, the law is crazy.

The District Attorney turns to a seated guest in his private office, the Honorable Judge Bannerman (William Paterson) of the Appellate Court (who also teaches Constitutional Law at the University of California at Berkeley), for his opinion on the case. Bannerman concludes that Callahan used unreasonable search and seizure and therefore the evidence acquired would be inadmissible. Also, Callahan's methods of physical torture and abuse to obtain a confession, and his lapse in reading the suspect his rights are further problems:

The search of the suspect's quarters was illegal. Evidence obtained thereby, such as that hunting rifle, for instance, is inadmissible in court. You should have gotten a search warrant. I'm sorry, but it's that simple...The court would have to recognize the police officer's legitimate concern for the girl's life, but there is no way they can possibly condone police torture. All evidence concerning the girl - the suspect's confession, all physical evidence - would have to be excluded.

Exasperated that he has violated the suspect's rights under four Constitutional amendments, Harry vehemently wonders what they can pin on the savage criminal and how they could possibly obtain justice: "There must be something you can get him on," but the Judge rejects any case against him. Harry defends the victim's rights, certain that the killer will continue to terrorize innocent citizens:

Judge: Without the evidence of the gun and the girl, I couldn't convict him of spitting on the sidewalk. Now, the suspect's rights were violated, under the Fourth and Fifth and probably the Sixth and Fourteenth Amendments.
Callahan: And Anne Marie Deacon, what about her rights? I mean, she's raped and left in a hole to die. Who speaks for her?
District Attorney: The District Attorney's office, if you'll let us. I've got a wife and three kids. I don't want him on the streets any more than you do.
Callahan: (as he turns to leave) He won't be out that long.
District Attorney: What is that supposed to mean?
Callahan: I mean sooner or later he's gonna stub his toe and then I'll be right there.
District Attorney: This office won't stand for any harrassment.
Callahan: You know, you're crazy if you think you've heard the last of this guy. He's gonna kill again.
District Attorney: How do you know?
Callahan: 'Cause he likes it.

On a street in the city, the long-haired Scorpio limps (after the stab wound, he lurches wherever he walks or runs) past a plywood barrier near a playground painted with black graffiti: DOWN WITH PIGS. A closeup of his waist reveals, ironically, that he wears a mis-shapen and twisted (literally and figuratively) 'peace symbol' belt buckle - an ubiquitous symbol of the peace-loving hippies and anti-war movement of the late 1960s. Obsessed to catch Scorpio 'stubbing his toe,' Callahan shadows the released killer, as he makes the rounds of the city - and ventures into the Red Light district at the Roaring 20's Club featuring topless dancers. Later, Scorpio contacts a black man and hires him (for "$200 dollars worth...every penny's worth") to beat his face and body to a nasty-looking, bloody pulp - as a way to get even with the city's police force for denying him the ransom money he demanded. Specifically, he wants to retaliate against Inspector Callahan and charge him with police brutality. As he is wheeled down a corridor, the heavily-bandaged Scorpio tells reporters for the local news that he is being harrassed, for no apparent reason, by the San Francisco police - he specifically identifies and frames Callahan as the perpetrator of the assault - to have him suspended:

They tried to frame me with the Deacon girl murder, and now they're trying to murder me - and look at me, just look at me. I'm supposed to be innocent until proven guilty and just look at what they did to me. Everywhere I go, cops follow me - and just look at me.

The statements are run on the four o'clock news, and are set to be printed in the San Francisco Chronicle. To the Police Chief, Harry admits conducting surveillance on Scorpio in an unofficial capacity ("on my own time") but denies beating him up "because he looks too damn good, that's how." As Scorpio had hoped, the Chief issues a restraining order toward Callahan - no more interference with the suspect. Callahan visits his recuperating partner Chico who is in physical therapy and has recurring second thoughts about being on the police force. He considers quitting and not returning to the life-threatening profession: "I've been doing a lot of thinking about it. I have a teaching credential and I figure, what for, you know?" Chico's blonde wife also worries about her husband's safety amidst the scum of the city: "I thought I could take it...Whatever it takes to be a cop's wife, I'm just not sure I'm making it. He really tries and these bastards, you know, Pig this, Pig that. Oh, but maybe it's when I watch him walk out that door at night, and I think, what if this is the last time I ever see him again." Even Harry counsels her: "I understand, you know, him quitting. I-I think he's right. This is no life for you two," although he admits he is at a loss for knowing why he still remains in the force: "I don't know, I really don't." A short while later, Scorpio (with a bloodied and bandaged face that makes him look increasingly more repugnant) robs a liquor store one evening that has already a long history of frequent robberies ("fourteen times the last three years"). He clobbers the much-robbed but armed proprietor (James Nolan) on the side of the head with a bottle of Seagram's that he has just purchased, takes the man's gun and another liquor bottle, and rushes out of the store. And then the next day, the leering and malignant Scorpio chooses more innocent victims when he hijacks a yellow schoolbus with seven children as it makes its afternoon rounds [in Sunset Heights]. He jumps aboard, impersonates a bus inspector, and then terrifies the female driver (Ruth Kobart) of the bus with a gun pointed at her mid-section: "Hear me, you old hag, I'm telling you to drive or I'll decorate this bus with your brains." He turns around and encourages the schoolchildren to sing. One fresh-faced youngster starts singing "Old MacDonald's Farm" and the rest of the happy kids innocently join in the chorus. Meanwhile, Harry Callahan is summoned to San Francisco City Hall, where he climbs the steps to the Mayor's Office, and is joined there by Lt. Bressler. The Mayor has already responded to another ransom note (delivered at 8 am that morning) from Scorpio:

To the City of San Francisco - You have double-crossed me for the last time. I'm warning you to have my $200,000 dollars in a jet airplane ready and waiting. I will call the Mayor's Office at one o'clock and tell you about the hostages who I will be happy to kill if you don't do exactly what I say. Scorpio.

Scorpio calls and informs the Mayor that he has just hijacked a Deichsel Charter Service school bus and kidnapped seven children and the bus driver - "I've got the kids. You start screwing around, the kids start dying." Holding the city hostage a second time, he orders the preparation of a jet plane from the Santa Rosa Airport with ransom demands of $200,000, and then alerts them to his terrorist plan:

I'm going to turn off on the Sir Francis Drake Blvd. on my way to the Santa Rosa Airport. I don't want to see any police cars, helicopters, whatever. Now if you got the guts to play this game by the rules, the kids will have a nice little plane ride.

The Mayor guarantees the criminal safe passage to the escape plane: "I guarantee you you will not be molested in any way. I give you my word of honor on it." A second time, Callahan is asked to deliver the ransom money to meet the blackmailer's demands, and he explodes in anger before refusing to do the Mayor's or Police Chief's bidding:

Callahan: When are you people gonna stop messing around with this guy. He's gotta be stopped now.
Mayor: He's got a busload of kids and I can't take that chance. I gave my word of honor on it, and he will not be molested - and that's a direct order, Callahan!
Callahan: Well, you can just get yourself another delivery boy.

He chooses to pursue and stop Scorpio this time - on his own terms. In the final, hijacked school bus sequence, the bus passes the Bison Paddock [in Golden Gate Park]. When the bus approaches within hearing distance, the children are now singing "Row Your Boat." The bus crosses the Golden Gate Bridge heading toward Marin County, where it drives through a tunnel [the Waldo Tunnel on Hwy. 101 with colorful rainbow entrances]. The warped, frightening and vicious monster begins to terrify the children by slapping them and exhorting them to sing: "All your mothers are gonna die if you don't start singing. I'm gonna kill all your mothers." They turn off the highway at a sign reading: SAN QUENTIN, SIR FRANCIS DRAKE BLVD." [Exiting here is about 45 minutes too soon if one is traveling to the Santa Rosa Airport. This is the exit for the Richmond/San Rafael Bridge.] Against orders, 'Dirty Harry' has pursued the killer as his personal vendetta. He is positioned on a wooden railroad trestle above Sir Francis Drake Boulevard - waiting there for the right moment to jump onto the roof of the moving bus. Scorpio is aghast at the sight of his sturdy, unyielding nemesis - Callahan:

Jesus. What the hell is he doing up there?

[Significantly, Scorpio hints at the religious subtext in the film by saying 'Jesus' immediately after seeing Callahan.] Scorpio shoots his pistol at the roof of the bus in a crazed attempt to hit the detective. After the bus driver screams, faints and collapses, and then is pushed from the driver's seat, the killer takes the wheel, sideswipes a VW bug, and then swerves the bus to try to dislodge Callahan from atop the bus. When the vehicle veers and crashes into the gates of the Hutchinson Co. Crushed Rock quarry plant [an area called Larkspur Landing], Callahan is thrown from the bus. Scorpio escapes through the buses' rear emergency exit and runs into the gravel plant. Through dusty corridors where the crushed rock is being conveyed, the cop chases and tracks after his prey, exchanging gunfire several times. Their pursuit leads them to a small pond behind the facility. There, Scorpio grabs a young boy (Stephen Zacks) who is fishing, shields himself, and points a gun to the boy's head, laughing madly and gleefully while threatening: "I'll blow his brains out." But Callahan won't surrender and drop his weapon. The accurate marksman narrowly misses the boy with one shot that severely wounds Scorpio in the upper left arm - this allows the hostage to escape. Harry walks up slowly to Scorpio and stands above him with his .44 Magnum for their final showdown during the manhunt. Gritting both his teeth and jaw, 'Dirty Harry' gives him a grim choice, a repeat of his litany to the bank robber: surrender, or gamble ("feel lucky") by reaching for his own gun, hoping that Harry is out of ammunition:

I know what you're thinkin', punk. You're thinkin', did he fire six shots or only five? And to tell you the truth, I forgot myself in all this excitement. But bein' this is a .44 Magnum, the most powerful handgun in the world, and it'll blow your head clean off, you could ask yourself a question. Do I feel lucky? Well, do ya, punk?

The hippie psycho-sadist makes his choice and reaches for the gun - but there is one more bullet in Harry's gun, and Scorpio is executed and shot dead - in cold blood. His body is propelled backward into the small lake. Callahan walks to the edge of the wooden platform above the water to gaze down at the murderer's bloodied corpse floating and slowly sinking below him. After having found retribution his own extra-legal way by exterminating the heartless and sick terrorist, without following bureaucratic police procedures, he thoughtfully hurls his police badge (Inspector 2211, SF Police) into the stagnant pond with the body and then walks away. Knowing that he will ultimately be reprimanded and fired for his action, the unrepentant Harry 'throws away' the symbol of his future police career in disgust.

[Note: This scene pays specific homage to the final scene of High Noon (1952) when the lone Marshal contemptuously discards his badge in the dust after being betrayed by the entire Western community.]

The film both begins and ends with the images of a policeman's badge. The camera pulls way back, another helicopter shot, as the approaching sounds of police sirens are heard on the soundtrack.