Sudden Impact

A college-age artist, Jennifer Spencer, and her sister are raped by a group of young men, after being betrayed by female friend Ray Parkins. The brutal rape leaves Jennifer's sister in a vegetative state from the physical and emotional trauma. Ten years later, Spencer seeks revenge on the attackers. She kills one of the rapists (George Wilburn) with two shotsâone in the groin and one in the headâfrom a .38 Colt Detective Special revolver. Spencer then leaves San Francisco because of the subsequent police investigation. Once relocated to the town of Santa Cruz, Spencer begins restoring its boardwalk's historic carousel near the beach where the rapes occurred.
Meanwhile, San Francisco Police Department Homicide Inspector Harry Callahan is frustrated when a liberal judge yet again dismisses a case of his due to what she sees as unreasonable search and seizure. Later, at his favorite diner, the inspector interrupts a robbery and kills most of the criminals. When the surviving robber takes a hostage, Callahan targets the man with his .44 Magnum and challenges him to "Go ahead, make my day". The criminal surrenders. Callahan later causes powerful crime lord Threlkis to suffer a fatal heart attack at his granddaughter's wedding reception when Callahan threatens him with prosecution in a murder case.
Lieutenant Donnelly, Harry's supervisor and other angry senior officers call Callahan in. They cannot fire or suspend the notorious inspector because, as the police commissioner admits, his "unconventional methods ... get results," albeit with many deaths and bad publicity for the department. They instead order him to take a vacation, which Callahan spends target shooting with his .44 AutoMag and shotgun-armed partner Horace. But Callahan's relaxation is short-lived, as four of Threlkis's hitmen attack him. The inspector dispatches three, and the other narrowly escapes. The suspect from the dismissed case and his friends also attack Callahan, throwing two Molotov cocktails into Callahan's car. He retrieves an unbroken firebomb and throws it at the attackers' car, causing the punks to swerve and drive into the bay. Lieutenant Donnelly immediately sends the inspector to San Paulo to investigate the murder of the man Spencer killed. While the victim is from there, the assignment is also to protect both Callahan and civilians. As Donnelly notes, "People have a nasty habit of getting dead around you."
Upon arriving in sleepy Santa Cruz, Callahan chases down a would-be robber. The reckless hot pursuit using a commandeered vehicle draws the anger of the local police. While jogging with his bulldog Meathead â a present from Horace â Callahan accidentally runs into Jennifer Spencer. She is less than thrilled. Upon returning to his motel, Callahan is targeted by the surviving Threlkis hitman. The inspector kills him after being warned of his presence by Meathead. Meanwhile, Spencer kills a second rapist, Kruger, at the beach. Callahan recognizes the modus operandi, but local police chief Lester Jannings refuses to work with the famous "big city hotshot."
Callahan learns that the victims and local figure Ray Parkins are friends of Jannings' son, Alby. Parkins figures out that the rapists are being targeted and warns two of them (Tyrone and Mick). After fighting Kruger's uncooperative brothers-in-law, Eddie and Carl, Callahan meets Spencer again â this time, at an outdoor cafe. Over drinks, he learns that she shares his emphasis on results over methods when seeking justice. But, the inspector adds the caveat " 'til it breaks the law." He then reveals that he is investigating the San Francisco murder of George Willburn, which rattles Spencer.
Callahan visits Tyrone's home and finds him dead, yet another victim of Spencer's vigilantism. Mick stays at Parkins' home, where both await a probable attack. When the inspector visits them for questioning, Mick attacks him. After Callahan subdues Mick and takes him to the police station, Spencer arrives and guns down Parkins, who had set up Spencer and her sister for the gang-rape. Callahan and Spencer meet again and have sex together. But on his way out he notices Spencer's car (which he had seen earlier at Parkins' house). He goes back there and finds Parkins' body. Eddie and Carl bail Mick out of jail. Meanwhile, Horace arrives at Callahan's motel to celebrate the easing of tensions in San Francisco. However, he meets Mick and his henchmen instead, who have been waiting in Harry's motel room. Horace is killed, Meathead is neutered by switchblade, and Mick finds Callahan. The inspector is brutally beaten and thrown into the ocean.
Meanwhile, Spencer arrives at the Jannings home with the intention of killing Alby, who was one of the rapists. She finds Alby Jannings is catatonic; a guilty conscience caused him to attempt suicide via a car crash that left him with permanent brain damage. Chief Jannings admits that to protect his reputation and his only child, he "fixed" the crimes and failed to jail the guilty parties. He convinces Spencer to spare Alby's life and promises that Mick, whom he does not know is free, will now be punished. Mick and the others capture Spencer and kill the chief with her .38.
Callahan survives Mick's assault and retrieves his powerful AutoMag from the motel. Enraged at what Mick's gang have done to Horace and Meathead, Callahan sets out after them. Mick's gang brings Spencer to the Santa Cruz Beach Boardwalk for another rape, but she escapes to the carousel. They recapture her, but are startled by the inspector's apparent return from the dead. After killing Eddie and Carl, Callahan chases Mick, who absconds with Spencer atop the Giant Dipper rollercoaster ride. The inspector reiterates his famous challenge "make my day"âthis time to Mick. When Mick laughs at Callahan, Spencer uses the diversion to break away. Mick is left wide open for Callahan to shoot. He aims and drops Mick, who plunges through the carousel's glass roof to a grisly death, impaled on a carousel unicorn.
The police arrive and find Spencer's .38 on Mick; ballistics, Callahan states, will prove that "his gun â¦ was used in all the killings." A compassionate Callahan and a vindicated Spencer leave the crime scene together.

Question: Why did Lieutenant Donnelly immediately sends the inspector to San Paulo?
Answer: to investigate.