The Texas Chainsaw Massacre Part 2

Set in 1986, 13 years after the events of the first film, two rowdy high school seniors, Buzz and Rick, race along a desolate stretch of Texas highway, en route to the OU-Texas football game at the Dallas Cotton Bowl. They are heavily intoxicated and use their car phone to call and harass on-air radio DJ Vanita "Stretch" Brock (Caroline Williams). Unable to convince them to hang up, Stretch is forced to keep the line open. Buzz and Rick encounter a large pickup truck which runs parallel to them on a remote bridge. Suddenly, Leatherface (Bill Johnson), wielding a chainsaw, emerges from the back of the truck and proceeds to attack Buzz and Rick. After a short struggle, Rick tries to shoot Leatherface with a .44 Magnum revolver, but misses his target. Leatherface then slices off part of the driving Buzz's head, and the car ends up crashing and killing Rick.
The following morning, Lieutenant Boude "Lefty" Enright (Dennis Hopper), former Texas Ranger, and uncle of Sally Hardesty and her invalid brother Franklin, who were victims of Leatherface and his family years earlier, arrives at the scene of the crime to help solve Buzz and Rick's murders. Lefty has spent the last thirteen years investigating his niece and nephew's disappearances while investigating reports of mysterious chainsaw killings across Texas. Although regarded with disdain by his peers, Lefty is able to convince the local newspaper to print a tiny article about his quest for justice. The article captures the interest of Stretch, who brings him a copy of the audio tape which recorded the attack on the two teenagers. Initially mortified, Lefty asks Stretch to play the tape on her nightly radio show so the law enforcers and the people will have to listen to him.
As the sounds of the horrible attack echo across the airwaves of Texas, Leatherface's family arrive at the radio station. While preparing to leave for the night, Stretch finds Chop Top (Bill Moseley) (who was stationed in Vietnam during the first film and is the twin of the Hitchhiker from the first film), waiting in the lobby. When she tries to get rid of him, Leatherface emerges from the darkness. Horrified, Stretch locks herself behind the metal door of a storage closet, holding off Leatherface until he comes through the wall. Meanwhile, Stretch's co-worker L.G. (Lou Perryman) arrives, but is beaten badly with a tack hammer by Chop Top. As Leatherface approaches Stretch, about to attack, she does some fast talking and charms him into sparing her. After a moment of distraction, Leatherface restarts his chainsaw and tears off through the studio slashing at walls, furniture and studio equipment, but leaves Stretch alive. He returns to the reception area where he leads Chop Top to believe that he has killed Stretch. Leatherface and Chop Top haul the mortally wounded L.G. off to their home, followed by Stretch, who winds up trapped inside the Sawyer home, which is actually an abandoned carnival ground decorated with human bones, multi-colored lights, and carnival remnants.
Lefty soon turns up with three chainsaws of his own and begins to carve up the home in a rage shortly before he finds the remains of his aforementioned nephew, Franklin. Stretch watches as Leatherface skins LG's face and parts of his body, but blows her cover. Leatherface, recognizing her, puts LG's face and hat on Stretch before tying her arms and leaving, to which LG wakes up and frees her before dying. Drayton (Jim Siedow) finds Stretch roaming the grounds and the family capture her. Lefty eventually finds her being tortured at the dinner table and saves her. Drayton tries to bribe Lefty with money, but Lefty slashes Drayton's back side with the chainsaw, and frees Stretch. A battle between Lefty and the Sawyer family ensues, ending with a chainsaw duel between Leatherface and Lefty. As a wounded Drayton commentates from under the table, Lefty gains the upper hand and impales Leatherface in the stomach. In the end, Lefty and most of the Sawyer family (Leatherface, "Grandpa" and Drayton) are apparently killed when a grenade (which Drayton recovers off of the Hitchhiker's preserved corpse) goes off prematurely. Only Chop Top and Stretch escape, where they have a final battle in a carved-out rock tower that overlooks the property.
Despite being slashed several times with a straight razor, Stretch grabs a chainsaw held by the mummified remains of the family's grandmother in a ritual shrine in the rock tower. Stretch then gets the upper hand on Chop Top, as she cuts him with the chainsaw, causing him to fall off the tower to a presumed death. The final shot shows Stretch going crazy and swinging the chainsaw similar to the first film.

Question: WHO restarts his chainsaw and tears off through the studio slashing at walls?
Answer: Leatherface