Foul Play

Recent divorcÃ©e Gloria Mundy (Goldie Hawn) is a San Francisco librarian. While attending a party, she is encouraged by a friend to leave herself open to new experiences. On the way home, Gloria picks up an attractive man named Bob "Scotty" Scott (Bruce Solomon) when she encounters him and his disabled car on Highway 1. She impulsively accepts Scotty's invitation to join him at the movies that evening, and before they part ways he asks her to take his pack of cigarettes in order to help him curb his smoking. Unbeknownst to her, Scotty has secreted a roll of film in the pack. That evening, a seriously wounded Scotty meets Gloria in the theater and warns her to "beware of the dwarf" before dying. When his body mysteriously disappears while Gloria seeks help from the theater manager, she is unable to convince anyone of what has transpired.
At the end of the following work day, Gloria is attacked in the library by albino Whitey Jackson (William Frankfather). She manages to escape and seeks refuge with Stanley Tibbets (Dudley Moore), a would-be ladies' man who assumes she is picking him up to have sex. Shocked by his misunderstanding, she flees and returns to her apartment, where she is attacked by a man with a scar who demands the cigarette pack Scotty had given her. When he attempts to strangle her with a scarf, Gloria stabs him in the stomach with a pair of knitting needles and calls the police for help. When her attacker tries to stop her, he is killed by Whitey through the kitchen window, and Gloria faints. When she awakens, all traces of what has happened have disappeared, and she is unable to convince two San Francisco policemen, Lt. Tony Carlson (Chevy Chase) and his partner Inspector "Fergie" Ferguson (Brian Dennehy), or even her landlord Mr. Hennessy (Burgess Meredith) that she was attacked.
Gloria is abducted by Turk Farnum (Ion Tedorescu), the chauffeur of a limousine in which she earlier had seen Whitey riding, but she manages to subdue him with Mace and brass knuckles given to her by her friend and fellow library employee, Stella (Marilyn Sokol). Later, Tony takes her to his Sausalito houseboat, where the two become involved romantically. Upon further investigation, Tony discovers that a contract killer named Rupert Stiltskin (alias "the Dwarf") was under investigation by an undercover detective named Bob "Scotty" Scott, who had received a tip that a major assassination would take place in the city on a certain night. Tony is now assigned to protect Gloria from her would-be killers.
When Tony and Fergie discover that the limousine is registered to the Archdiocese of San Francisco, they visit the office of Archbishop Thorncrest (Eugene Roche), unaware that the man they're interviewing is in fact the Archbishop's twin brother Charlie, who is involved in a plot to assassinate Pope Pius XIII (played by prominent San Francisco businessman Cyril Magnin) during his upcoming visit to San Francisco. Charlie has murdered his twin in order to impersonate him. The following day, Rupert kidnaps Fergie and uses him to lure Gloria into a trap. She manages to hide in a massage parlor, where she encounters Stanley yet again, but then is found and abducted by Jackson and Stiltskin.
At Gloria's request, Stella has researched an organization known as the Tax the Churches League, and discovered that the League is a radical fringe group, founded by one Delia Darrow and her husband. For the Darrows, organized religion is a corrupt, greedy sham involving powerful billion-dollar corporations. Stella gives the results of her findings to Tony, who returns to the Archbishop's residence with Mr. Hennessy. Sneaking into the wine cellar, Tony discovers the imprisoned Fergie, who informs him that Stiltskin was hired by the Darrows to assassinate the Pope during a performance of The Mikado at the San Francisco Opera House that evening. Tony is attacked by Rupert and kills him in self-defense by toppling shelves of wine upon him, but then is held at gunpoint along with Gloria by the fake archbishop's assistant Gerda Caswell (Rachel Roberts), who is really Delia Darrow.
Darrow then details her "contingency plan" to eliminate the Pope: If His Holiness is not yet terminated at the end of Act I, Whitey Jackson will open fire from one of the auditorium's two organ bays ("He will also open fire should the Pope unexpectedly leave his seat, or if the police arrive in the auditorium," Darrow explains). Mr. Hennessy knocks out Charlie and defeats Delia in a martial arts duel, and Tony and Gloria race to the Opera House, having some unusual problems along the way (such as crashing into an Italian restaurant and commandeering a limo carrying a pair of Japanese emigres). After making it backstage, Gloria is grabbed by Jackson, who kills one of several security guards who have joined the pursuit. An enraged Gloria attempts to attack Jackson, who simply shoves her to the floor. This gives Tony the room he needs to shoot the albino, thus thwarting the plan to kill the Pope. As the performance ends, Gloria and Tony are revealed onstage along with the now-dead bodies of Jackson and the guard, but the Pope, who seems not to have noticed anything unusual, leads the audience in applause for the cast, the orchestra, and the conductor - Stanley Tibbets.

Question: Who murdered his twin brother in order to impersonate him?
Answer: Charlie