<P> Dan is a controlling father to Nathan, who is now the Ravens' star player, but has nothing to do with Lucas . When Lucas joins the Ravens, Dan encourages Nathan to give his half - brother a hard time . Dan puts so much pressure on Nathan that Nathan takes drugs to enhance his basketball performance, leading to him collapsing on the court . When Deb finds out, she asks Dan for a divorce . When Dan's parents come to town for Dan's birthday, it is revealed that Dan's father Royal put similar pressure on Dan and that Dan faked the extent of an injury he suffered in college in order to give up basketball . Dan also has an uneasy relationship with Keith, due to Keith's continuing friendship with Karen . When Keith crashes the car he is driving with Lucas inside, Dan pulls Lucas from the car and saves his life, leading to a temporary truce with Karen . Keith is left in financial difficulty due to Lucas's medical bills and Dan offers to buy Keith's garage from him while Keith continues to run it . However, it soon becomes clear that Dan will be running the garage in his own way and Keith quits . After being rejected by Karen, Keith turns to Deb for comfort and they have a one - night stand . On walking in on them in bed together, Dan tells Keith that he is no longer his brother . Dan is about to sign his divorce papers to Deb when he suffers a heart attack . When Deb finds Dan on the floor, Dan tells her "you'd better hope I die ." </P> <P> After his heart attack, Dan claims to be a changed person and tries to get closer to Lucas . Dan and Deb are united in their disapproval of Nathan's marriage to Haley . Dan claims to have forgiven Deb and Keith for their fling and a guilty Deb allows Dan to live with her while he recovers . It becomes clear that the new Dan is an act when he lies to Deb after being given a clean bill of health and it is revealed that Keith's new girlfriend Jules was actually hired by Dan to seduce his brother . On discovering that he has the same heart condition as Dan, Lucas agrees to move in with Dan on the conditions that Dan pays for Lucas's medication and keeps this from Karen, and also that Dan leaves Keith and "Jules" alone . Dan keeps his promises but Karen discovers the truth about Jules and threatens to tell Keith, leading to Jules leaving Keith at the altar . Dan is delighted at this result and, after knocking down the groom on the wedding cake, looks at Deb saying "one down, one to go". On discovering what Dan did, Keith confronts Dan at the dealership and attacks him . Before leaving town, Keith tells Dan that he has nothing left to lose, but Dan does . When Nathan and Haley's marriage is in trouble, Dan is quick to pounce, and gets Nathan to sign annulment papers and move back in with him and Deb . However, Deb wants Dan out of their lives for good, especially after learning that Dan told Nathan that it is his fault that Deb is now addicted to pills . Lucas continues to live with Dan in order to bring down his father once and for all . He finds cash and an incriminating ledger in the attic of the dealership and discovers that Dan has been making money illegally by changing the amounts on bills and pocketing the extra cash . However, Dan has made Deb the co-owner of the dealership, meaning that she would be incriminated too . Dan then reveals he left the cash and ledger for Lucas to find as a test of Lucas's loyalty, which Lucas failed, and so Dan severs all ties to Lucas, even cutting off his son's heart medication . Dan also sabotages Karen's relationship with her business lecturer Andy by walking into one of Andy's classes and telling everyone that Andy is sleeping with Karen, which leads to Andy losing his job . Dan then tries to have Andy deported back to New Zealand . When Karen angrily confronts Dan at the dealership, Dan grabs her and forcefully kisses her, saying "isn't that was this is really about?" At the end of the season Dan falls unconscious after drinking a poisoned bottle of whisky that was left for him with a note saying "for everything you've done". The dealership is then set on fire with Dan inside . </P> <P> Dan survives the fire, but the dealership is destroyed . Dan at first thinks it was Lucas who tried to kill him when he remembers seeing him in the fire, but it is revealed that Lucas saved him . Wanting access to the fire investigation, Dan runs for mayor of Tree Hill . His family - based campaign includes having Deb pretend to love him in exchange for a final divorce . This ploy works and Dan is elected mayor . As mayor, Dan gains access to CCTV showing Keith buying the whisky used to drug Dan, and when Keith returns to town Dan has him arrested on suspicion of his attempted murder . Although the police release Keith due to lack of evidence, Dan still believes that Keith was the perpetrator, and things become worse when Keith announces that he is going to marry Karen and adopt Lucas . One day at Tree Hill High, Jimmy Edwards takes a gun to school and fires it, causing a lock down . Keith persuades Dan as mayor to let him go into the school to talk to Jimmy, but Jimmy commits suicide by shooting himself in front of Keith . Dan then gets into the school, picks up the gun and shoots Keith, killing him . Jimmy gets the blame for Keith's death as it is assumed that he shot Keith before turning the gun on himself . Dan convinces himself that Keith deserved what he got as he started the war with Dan . Nevertheless, Dan becomes haunted, seeing visions of Keith as a child everywhere, and this has a profound effect on him . Realizing he has to change his ways he tries to get closer to Nathan, telling his son that he is proud of him and that he loves him . Haley then gives Dan a second chance by inviting him to her and Nathan's second wedding . At the ceremony Deb tells Dan that it was her, not Keith, who tried to kill him in the fire . Dan goes to Keith's grave and breaks down . Dan then apologizes to Karen for how he treated her and Lucas and she reveals that she is pregnant with Keith's child . Dan takes her in his arms promising to be there for her this time . He then goes home and discovers that someone has written "MURDERER" on his wall . </P> <P> Dan tries to make amends for Keith's death by looking after Karen . However, he still sees messages everywhere calling him a murderer, and wonders if it is all in his head . Meanwhile, Nathan is in deep debt and asks Dan to help him . Dan refuses and Nathan goes to a loan shark, Daunte, instead . Daunte forces Nathan to shave points in a basketball game and then demands that Nathan lose the State Championship . On discovering the trouble that Nathan is in, Dan confronts Daunte and offers to pay him off, but Daunte gets Dan to back down by threatening Nathan, Lucas, the pregnant Haley and Karen . When the Ravens win the State Championship, Daunte runs Haley over and crashes into a construction site . Nathan pulls Daunte out of the car and beats him, before realizing he is dead . Dan takes the fall for Nathan and is arrested . Dan plans to plead guilty to Daunte's murder in order to be punished for Keith's death, but the coroner's report shows that Daunte was already dead when Nathan pulled him out of the car . Dan is released and the experience brings him and Karen closer together, as Karen admires what Dan was willing to do for his son . Dan and Karen begin to come together romantically, attending the school prom together as chaperones, but Dan continues to receive text messages and notes accusing him of killing his brother . Dan discovers that the person sending the messages is Abby Brown, a student who witnessed the shooting . Dan then visits Abby and her mother and tries to explain why he killed Keith, saying "Karen was mine, she was supposed to be mine". Abby leaves Tree Hill for good, but not before telling Lucas what she knows . Lucas walks in on Dan and his mother kissing and attacks Dan, shouting that he killed Keith, but Karen refuses to believe him . Lucas then goes to the police, but Dan has got there first and told them that Lucas is just trying to sabotage Dan's relationship with Karen . On learning from Haley that Deb has a gun, Lucas steals the gun and confronts Dan in front of Karen, causing her to collapse . Lucas fires a warning shot to make Dan leave, before rushing the unconscious Karen to hospital . After learning from Deb that Dan killed Keith, Nathan confronts Dan and tells him that he will never be a part of his grandson's life . After Karen's daughter is born by c - section, Dan visits his new niece in the hospital, before turning himself in to the police . </P>

Who set the fire in one tree hill