Curtains

Samantha Sherwood, a beautiful actress and muse for director Jonathan Stryker, has herself committed to a mental institution as method preparation for the titular role of a mentally unstable woman in a film called Audra. Once finding out Stryker is letting a new group of girls audition for the role of Audra, she escapes the asylum for revenge.
One of the girls invited to audition, fledgling actress Amanda Teuther, has a dream that while driving to the audition, she is stopped by a large porcelain doll standing in the middle of the road; when she leaves her car to move it, she is run over. She awakens from her dream, only to be stabbed to death in her apartment.
The next day, we are introduced to the five other women auditioning for the part of Audra who have all been invited to Stryker's mansion. They are comedian Patti O'Connor, veteran actress Brooke Parsons, dancer Laurian Summers, musician Tara DeMillo, and professional ice-skater Christie Burns. A caretaker named Matthew is also introduced. Samantha appears at the house uninvited during dinner. The girls spend their first night in the mansion getting acquainted; Tara has sex with Matthew in a jacuzzi and Christie reluctantly is seduced by Stryker.
The next morning, Christie goes to a nearby pond to ice skate. She notices a small hand protruding out of the snow at the edge of the pond, and uncovers a porcelain doll. She is then attacked and decapitated with a sickle by someone in a grotesque hag mask.
Later that day, after the killer watches a drunk Matthew ride away on a snowmobile, Patti is given an impromptu audition with Stryker and nearly bombs, due to nerves. While Tara and Laurian are auditioning, Brooke discovers Christie's severed head in a toilet bowl. She frantically informs Stryker of what she's seen, but when they go back to the bathroom, the toilet is empty. Exploiting Brooke's vulnerability, Stryker seduces the frightened actress. Meanwhile, Tara and Patti ponder Brooke's reason for claiming that Christie is dead, Tara suspecting foul play. At the same time, Laurian is stabbed to death while dancing in a room upstairs.
After having sex, Brooke and Stryker are both shot to death by a figure in a robe. The gunshot victims fall from a second story window, Stryker's body crashing through a window downstairs. Terrified at the sight of the corpse, Tara flees the mansion. Running past Matthew's corpse, Tara is chased by the hag through an expansive prop and costume warehouse on the property. After escaping the killer three times and discovering Laurian's corpse among a group of hanging mannequins, she is dragged into a ventilation shaft and killed.
A short time later, Samantha and Patti discuss Audra's insanity in the kitchen, over champagne. Samantha tells Patti about how Stryker left her in the asylum and eventually confesses to shooting Stryker and Brooke. Startled by the news of Stryker's death, Patti reveals that she murdered the others to win the part of Audra and stabs Samantha to death.
The epilogue consists of Patti (now committed in mental institution) performing a monologue from Audra to other patients in the mental institution.

Question: Who stabbed Samantha to death
Answer: Patti