Lucas Scott In Season 4, Lucas tries to get Brooke back, but she rejects him, feeling that the passion is no longer there. One day, he hurries to save Peyton from Internet stalker "Psycho Derek", and becomes considerably closer to her afterward. He also helps Karen, who is pregnant with Keith's baby, and plans on going to the University of North Carolina when he graduates so that he can be close to home in case she needs him. Dan also helps Karen with her pregnancy, wanting to make amends for Keith's death. After talking with Dan, Karen persuades Whitey to let Lucas play 15 minutes a game, so as not to let him miss out on something he loves. Brooke and Lucas try dating each other again, but realize that it is not what they truly want and is not what is meant to be, prompting Peyton to confess her feelings for Lucas. Lucas then discovers that Nathan is planning to throw the state championship game because of his debts. Lucas plans to prevent this and deliberately fails to take his heart medication in order to play better, but Nathan is inspired by learning that he is going to have a son and they win, with Lucas making the winning shot. During the celebration, Lucas, after receiving Brooke's blessing, sees Peyton and tells her that she is the girl he has been meant for. The two then share a long-awaited kiss. They become a couple at the after-party, but their happiness is short-lived when Haley gets hit by a car and Lucas tries to tell the paramedics what happened only to suffer a heart attack. As he is in the hospital, Lucas dreams that he is visited by Keith, who shows Lucas what life would have been like if he had been a lesser person. In the end, Lucas realizes that he has to go back to his life because he never told Peyton that he loves her. Lucas wakes up and begins a relationship with Peyton. After the failed attempt of prom in Tree Hill High, the group go on a rescue mission to save Mouth who has become stranded in Honeygrove. They all then crash the local Prom, where he and Peyton have sex with each other for the first time. He begins to investigate Keith's death, as the Keith in his dream suggested that Jimmy did not kill him, but he also starts getting closer to Dan, who tells Karen he wants a bigger part in Lucas's life. Lucas discovers the truth about Dan thanks to witness Abby Brown. He attacks Dan after walking in on him and Karen kissing and tells Karen that Dan killed Keith, but Dan convinces Karen that Lucas is delusional and needs help. Lucas then steals Deb's gun and confronts Dan in front of Karen, having set him up by sending him a message from "Abby". Karen collapses and Lucas fires a warning shot at Dan, telling him not to touch her. Karen is rushed to hospital with eclampsia and has an emergency c-section. Lucas is given a half-sister, who is named Lily Roe Scott when Karen regains consciousness. Later, Dan turns himself in for Keith's murder. Lucas graduates and gets, as a reward, his book (An Unkindness of Ravens) from his mother. That same day, he becomes an uncle with the birth of Nathan and Haley's son, James Lucas Scott, partly named after him. Lucas is named the godfather of James and announces that he will be assisting Whitey as Nathan's college basketball coach.

Question: when does lucas find out dan killed keith