LOS ANGELES, California (Reuters) -- Twenty-five years after the murder of former Beatle John Lennon, a Canadian-based film company is set to explore the mind of his killer in a movie starring Lindsay Lohan and Jared Leto, backers of the project said on Thursday.Leto, who played a heroin addict in "Requiem for a Dream" and a cocaine-snorting arms dealer in "Lord of War," has signed on to portray Lennon's killer, Mark David Chapman, in the upcoming independent film "Chapter 27."Lohan, the teenage "Mean Girls" star last seen in "Herbie: Fully Loaded," will play a fictional Lennon fan who befriends Chapman during the weekend he kills the musician outside his Manhattan apartment building.Leto, 33, and Lohan, 19, are rumored to be dating, but her publicist told Reuters only that the two have spent time in recent months "doing research for the movie together."The parts of Lennon and wife Yoko Ono have not been cast.Peace Arch Entertainment President John Flock, whose Toronto-based company is financing the picture, said the character of Lennon himself would get relatively little screen time as the movie focuses on Chapman in the days leading up to the murder.The role Lohan will play was created as a plot device to help filmmakers deconstruct Chapman and his motivation for killing the rock celebrity, Flock said."It's a psychological study of (Chapman)," Flock told Reuters. "I wouldn't call it a sympathetic portrayal of him, but you do kind of get into Chapman's head."Likewise, Flock suggested the murder itself would be depicted in a relatively circumspect manner. "It's the most significant event in the movie, but we're not planning on giving it much if any screen time."Chapman, currently serving a prison sentence of 20 years to life, shot Lennon to death outside the Dakota apartment building on December 8, 1980, hours after getting the former Beatle to autograph a copy of his newly released comeback album "Double Fantasy."Flock said the title of the film, "Chapter 27," is a reference to the 26 chapters in the J.D. Salinger coming-of-age novel "The Catcher in the Rye," which Chapman cited as his inspiration for the murder. Chapman has said he identified with the book's hero, who hated phonies, and gunned Lennon down because he thought him a hypocrite.Production on the film, the brainchild of first-time writer and director Jarrett Schaeffer, is set to begin January 16 in New York, with producers aiming for a commercial release late next year, Flock said.Copyright 2005 Reuters. All rights reserved.This material may not be published, broadcast, rewritten, or redistributed.