Saw VI

Two predatory lenders awaken on either side of a room split by a caged-in scale, wearing head harnesses with screws poised to pierce their temples. The one who sets more flesh weight upon their tray will survive. Eddie cuts fat from his torso, but Simone chops off her arm, and Eddie is killed when the timer expires. As he reviews the game's footage, Detective Lieutenant Mark Hoffman is called to the scene by FBI Agent Dan Erickson, who has found Peter Strahm's fingerprints. Also present is Lindsey Perez, whose survival was covered up by Erickson for her protection. They learn from Dr. Adam Heffner, the coroner who performed all of the autopsies for the case thus far, that the knife used to cut the jigsaw piece from Eddie's flesh was only used once before, on Seth Baxter. The agents intend to find the Baxter videotape to prove Strahm's involvement.
While at the hospital to meet with Simone, Hoffman is met by reporter Pamela Jenkins, who claims to have found something at the meatpacking plant. He later meets with Jill Tuck at her clinic and takes control of the games, and is given five envelopes from the box left to her in John Kramer's will, each containing photos of people to be tested. After he leaves, a flashback reveals that Kramer brought Amanda Young to Jill, who had deemed her a lost cause, as proof of his methods. A later flashback, as Jill delivers a package from the box to the hospital, shows that Jill met with Kramer at the plant hours before his death, where he gave her the box's key and his promise that she would be protected when the games ended.
William Easton, an insurance executive for Umbrella Health, meets with Debbie, the company's attorney, about Harold Abbott, who succumbed to heart disease after his coverage request was denied due to an application discrepancy. Hoffman abducts Easton from his office that night and brings him to an abandoned zoo, where he and his janitor, Hank, awaken in vises designed to tighten around their torsos each time they breathe into oxygen masks strapped to their faces. Kramer himself appears in a videotape and informs Easton that he has one hour to complete four tests and remove the bombs strapped to his limbs, or he will lose his family. Hank, a heavy smoker, is unable to hold his breath for long and is killed by the vise. The other tests force Easton to save his staff and associates, including Debbie, from their own traps, usually by choosing between them; this forces him to confront his own probability formula, which favors the healthy over the ill. It is shown that Kramer met Easton at the opening of Jill's clinic and took issue with his formula. After his cancer was diagnosed, Kramer's coverage request for an experimental Norwegian treatment was rejected by Easton.
The game is viewed by a woman named Tara and her son Brent from a cage below the observation room, which contains a tank of hydrofluoric acid and a switch marked "Live" and "Die". Pamela awakens in another cage on the other side of the room. During the game, Hoffman is called away by Erickson and Perez, who found the Baxter videotape and are having it unscrambled by an offsite technician. They inform him that abnormalities were found in Strahm's fingerprints, and Erickson eventually reveals their knowledge of Strahm's death. The moment his voice is unscrambled, Hoffman attacks and kills everyone in the room, plants fingerprints using Strahm's severed hand, and lights the room on fire to destroy the evidence.
He returns to the observation room and finds the letter he'd written to Amanda, in which he'd used his knowledge of her role in Jill's miscarriage to blackmail her into killing Lynn Denlon. The letter was found by Pamela and given to Jill, who uses it to ambush Hoffman as Easton reaches the end of his path with one second left, finding himself between the cages. It is revealed that Pamela is his sister, while Tara and Brent are Harold's family. Tara is informed by a videotape of Kramer that she can either kill Easton or free him using the switch; when she is unable to do so, Brent angrily shifts the switch and a bed of needles swings down and injects Easton's body with the acid, killing him. Jill restrains Hoffman and locks a new reverse bear trap to his head. She shows him the sixth envelope, which contains his photo, and leaves him with 45 seconds but no key. He escapes by breaking his hand and jamming the trap as it activates; he pulls his head free, ripping open his cheek, and the screen cuts to black as he screams.

Question: What is used to plant fingerprints
Answer: Straham's severed hand