Suspiria

Suzy (Jessica Harper) and Sara (Stefania Casini)
Suzy Bannion, an American ballet student, arrives on the airport in Munich, Germany, to enroll in the prestigious Tanz Dance Academy in Freiburg. Arriving late at night, and in the midst of a torrential thunderstorm, Suzy is unable to gain entry to the academy. However, she witnesses a young student, Pat Hingle, flee from the school in a state of abject terror. As Pat leaves, she calls out to someone just inside the building, though Suzy is unable to hear her words clearly over the raging storm. As Suzy makes her way to a hotel, Pat finds refuge at a girlfriend's apartment in the nearby town. Explaining to her friend that she has uncovered something terrible inside the Tanz Academy, Pat states that she is leaving in the morning. After locking herself in the bathroom, she is drawn to the window, where she sees the vague form of a shadowy figure lurking outside. Using a lamp to penetrate the darkness, a pair of inhuman eyes glare briefly back at her before disappearing. As she leans closer to the window, a withered but powerful arm smashes through the pane and smothers her against the glass. Hearing Pat's screams, her friend pounds desperately on the locked door, before running from the apartment to find help. In the bathroom, the black-cloaked attacker launches a vicious and relentless assault on Pat, stabbing his young victim repeatedly. As she lies drenched in blood and mortally wounded from multiple savage knife wounds to her heart, the sadistic killer slips a noose around her neck. In the room below, Pat's friend is running for the exit when a piece of glass falling from above narrowly misses her, stopping her in her tracks. She looks up just as Pat's body crashes through a large stained glass skylight and plummets into mid-air before the rope snaps taut, killing her. And on the ground below Pat's suspended body, lie the mutilated remains of her friend, lethally impaled amidst a maelstrom of jagged glass and twisted metal.
The following morning, upon Suzy's arrival at the academy, she is introduced to Madame Blanc, the vice-directress, and Miss Tanner, one of the instructors. She is escorted to the student's locker room, where she meets two fellow students, Sara and Olga, the latter with whom she has arranged to stay with off-campus. After a strange encounter with the academy's cook, Suzy faints during a lesson. Later that night, she awakens to discover that she has been moved into a dormitory room against her wishes. The doctors tell her that she is to be "medicated" with a glass of wine daily. Suzy befriends Sara after the two are roomed together. As the students prepare for dinner, hundreds of maggots fall from the ceiling. The students are told this was due to spoiled food being stored in the attic. The girls are invited to sleep in the practice hall overnight while the spoiled food and maggots are properly disposed. During the night, Sara identifies a distinctive whistling snore as that of the school's director, who is not due to return to the academy for several weeks.
The next morning, Tanner orders the school's blind piano player, Daniel, to leave the academy immediately after his guide dog bites Albert. Later that night, Sara overhears the teacher's footsteps and begins to count them whilst Suzy becomes drowsy and falls asleep. Elsewhere, while Daniel and his guide dog cross a plaza, Daniel senses a strange presence; suddenly, his seemingly calm dog lunges at Daniel and tears his throat out, killing him. The next day, Suzy recalls the words "iris" and "secret" from Pat's mumbling, when she first arrived at the academy. Later that night, Suzy and Sara go for a swim while Sara reveals to Suzy that she and Pat were close friends, and recalls that Pat had been "talking strangely for some time". The two girls search for Pat's personal notes, but they appear to have been stolen. Suzy suddenly becomes drowsy and falls asleep before Sarah flees after hearing footsteps. Sara is chased by an unseen pursuer and, thinking she will be able to escape through a window into another room, falls into a huge pile of razor wire. She struggles in anguish until a mysterious black-gloved hand of a dark figure appears and slits her throat.
The following morning, Blanc and Tanner inform Suzy that Sara has abruptly left the academy. Confused and suspicious, Suzy goes to meet one of Sarah's acquaintances, a psychologist, Frank Mandel, who explains that the academy was founded by Helena Markos, a cruel Greek Ã©migrÃ© who was widely believed to be a witch. Dr. Mandel's colleague, Professor Millus, then tells Suzy that a coven can only survive with their queen. Upon Suzy's return, she discovers that all of the students have gone to the theatre. She overhears the footsteps Sara identified before and follows them to Blanc's office. She suddenly recalls Pat's mumbling after discovering irises painted all over the walls of Blanc's office. After entering a hidden passage, she discovers Blanc, Tanner and the staff performing a ritual where they plot Suzy's death. Unseen, Suzy then turns to find Sara's body nailed to a coffin. Frightened, Suzy then sneaks into another room, where she accidentally awakens a shadowy figure who reveals herself as Helena Markos. She hears a laughing and demonic voice. Helena then orders Sara's nearby corpse to rise from the dead to murder Suzy. Suzy then stabs Helena through the throat with one of the room's decorative knives, which appears to kill her (she fades from view screaming) and Sara's reanimated corpse. Helena's demise causes the building to set alight. As the academy is slowly destroyed with the coven inside, Suzy manages to escape before the entire building catches fire.

Question: Who chases Sara?
Answer: An unseen pursuer