Hard Candy

The film opens with a sexually charged, flirtatious online chat between 14-year-old Hayley Stark and Jeff Kohlver, a photographer in his mid-30s. Jeff and Hayley meet at a coffeehouse, and he takes her back to his apartment. Hayley makes them both screwdrivers and asks him to take photographs. Before he can, Jeff gets dizzy, his vision blurs, and he falls to the floor unconscious.
When Jeff wakes, he is bound to a chair. Hayley explains she has been tracking him and drugged him because she knows he is a pedophile, child rapist, and murderer. Jeff denies these allegations, claiming he had innocent intentions. Hayley searches Jeff's house and finds his gun and safe. In the safe, Hayley finds "sick" pictures and a photo of Donna Mauer, a local girl who had been kidnapped and remains missing. Jeff denies involvement in Mauer's disappearance and succeeds in reaching his gun, but when he (still bound to the chair) attacks Hayley, she renders him unconscious by asphyxiating him with plastic wrap.
When Jeff wakes, he finds himself bound to a steel table with a bag of ice on his genitals. Hayley explains she will castrate Jeff. Jeff threatens, bribes and sweet-talks Hayley to dissuade her; when that doesn't work, he tries to get her sympathy by telling her he was abused as a child. Following the operation, Hayley leaves the kitchen, claiming to take a shower. Jeff struggles and frees himself. When he reluctantly checks the site of the operation, he realizes he is actually unharmed, and Hayley has elaborately faked his castration. He storms off in a rage to get Hayley in the bathroom, where the shower is running. Scalpel in hand, he attacks, only to find the shower empty. Hayley attacks him from behind, and as they struggle, Hayley incapacitates him with a stun gun.
Hayley poses as a police officer and asks Jeff's ex-girlfriend, Janelle, to come immediately to Jeff's house. Jeff regains consciousness to find that Hayley has bound his wrists and hoisted him to stand on a chair in his kitchen with a noose around his neck. Hayley makes Jeff an offer: if he commits suicide, she promises to erase the evidence of his crimes, but if he refuses, she promises to expose his secrets. The conversation is interrupted when a neighbor knocks on the front door, selling Girl Scout cookies. Hayley tells the neighbor that she is Jeff's niece; the neighbor leaves shortly afterwards. When Hayley returns, Jeff breaks free from his bindings and pursues her, eventually finding her on the roof of his house, where she has lured him. Hayley has brought her rope from the kitchen and fashioned it into a noose secured to the chimney. Hayley keeps Jeff at bay with his own gun.
Jeff finally confesses that he watched while another man raped and murdered Donna Mauer. Jeff promises Hayley that, if she spares his life, he will tell her the other man's name so she can exact her revenge. Hayley confesses that she knows his name and says, "Aaron told me you did it before he killed himself." Janelle arrives, and Hayley once again urges Jeff to hang himself, promising that she will destroy the evidence. Defeated, Jeff lets Hayley slide the noose around his neck, and takes the last fatal step off the roof. At the moment Jeff dies, Hayley says, "Or not." She then gathers her belongings and escapes through the woods. The film ends as Hayley walks down the road in her red hoodie.

Question: What does Jeff confess ?
Answer: Jeff confesses that he watched while another man raped and murdered Donna Mauer.