Who killed lestor in American beauty?

Answer 1

Lester is most defiantly killed by Frank (the neighbor). This is my favorite movie and I have watched it many times to make sure of this.
Here we go, Carolyn is walking to the house from the driveway and is thinking of using her gun...I suppose to kill Lester. As she is walking to the house the shot is already fired. People say she did it and that it was her gun and that Frank killed his own wife and the Ricky says "Mom" when he sees Lester is dead. All of that is incorrect. The following is what really happens:
Frank is confused and horrified at his realization that he himself is gay and the fact that he was turned down by the one man he had briefly shown this side to. He is so upset that he goes into his study and takes out one of his guns (the silver and black hand gun, third from the bottom, that ironically Carolyn has the same of). Frank, then goes to the Burnham house and shoots Lester. He heads back home and we see him soaking from the rain outside and splattered in Lester's blood. The shot then moves to the wall cabinet where Frank keeps his guns, and the gun (previously mentioned), third from the bottom, which we saw the barrel of in the scene where Lester is shot, is missing. We then see Carolyn, who has seen the body of Lester, in their room crying and looking at her purse with her gun in it. At this moment she is horrified that she herself was thinking about killing Lester and throws the purse in the hamper in attempt to "make it all go away"...she then grabs onto all his shirts hanging in the closet and sobs and realizes how much she actually did love him and can't believe she, herself, wanted to kill him. Lastly, when Ricky sees Lester dead (which is the most brilliant scene of the move....watch it again and notice the subtleties and you will know what I mean)....Ricky does not say "Mom"....he says "Wow" in a hushed tone.
There is your answer, I hope it answered all questions. :)