American Beauty/WMG

The plate Mrs. Fitts is holding when Ricky says goodbye is the Nazi plate.
Hey, she's holding a plate and we can't see the whole plate. Maybe Ricky's opening the cabinet wasn't really what set his Dad off - maybe it was really his mother rooting around (maybe even having taken the actual key), and his Dad assumed it was Ricky.

Ricky's Dad keeps his gay Porn Stash hidden in the same cabinet as the plate.
That's why he doesn't want Ricky sneaking around in there.

Buddy King's divorce was a ruse.
He "breaks up" with her just to screw (and manipulate), the female business competition, and she just keeps a low profile for a while - then they "make up". The older women are far more willing when they know they're taking the place of a younger, prettier girl. The "I'm about to go through an expensive divorce" line just lets him get off the hook at a moment's notice. This is how he became "The King". (And adds a lot to the "Who's the real estate king!!?!? scene.)

Ricky is actually Buddy "the Real Estate King" King's son.
Look at them - they both have the same sort of thick eyebrows. Mr. and Mrs. Fitts knew him a while back, and maybe Mrs. Fitts had an affair with him while Mr. Fitts was on assignment in the service. Mr. Fitts never found out and assumed he was the father - or knows he isn't but didn't complain because it kept up his hetrosexual appearances. Ricky knows he looks nothing like his "father", which is why he doesn't mind playing him. When they needed a house, of course Mr. Fitts went to their old aquaintence. Maybe the reason Mrs. Fitts is so out of it was buying the house dredged up a whole lot of memories.

Lester becomes a Time Lord.
Okay, that's out of the way.

Mrs. Fitts killed Lester.
It's always the quiet ones. Mrs. Fitts has very obviously become nothing but the shell of a suburban housewife, all about appearances with no internal personality whatsoever. In some ways, she's even more of Lester's opposite than Carolyn. She has no life outside pleasing her husband and taking care of her son, and both of these tasks are disrupted when Lester starts doing what he pleases. All of the implied abuse she takes from her husband would be for naught if he rethought his life and sexual identity, not to mention she would probably end up out of a home. By killing Lester, she felt she could restore the status quo of the neighborhood and make her husband happy by eradicating someone who had rejected him.

When Colonel Fitts comes home with Lester's blood on his shirt, it's because he was trying to stop her. There's an awful lot of blood to have been sprayed from an entry wound made by a handgun. Colonel Fitts came in just in time to see it happen, get some of the exit splatter, and pry the gun away before Mrs. Fitts caused anyone any more harm.

The police were never called - the murder was covered up, and they claimed Lester disappeared.
Everyone worked together to cover up the murder and split Lester's financial windfall (Let's say his company gave him a lump-sum rather than a paycheck). Why? Well, Mr. Fitts has a LOT of blood on him when he returns home. He did the cleanup. Claiming Lester had run off wouldn't be a stretch - he's been acting weird for a while: smoking dope, changing to a low-end job, lusting after a young girl...

Because everyone was planning on killing him in the first place: Angela threw herself at him so he had the chance for one last fling. Mr. Fitts threw himself at him to have the chance with another guy who couldn't blab about it later. Carolyn was the ringleader - it was her job to do it if Lester fought Mr. Fitts, that's why she was ready with her gun - that's why she's hugging his clothes rather than comforting her daughter or waiting for the police.

Angela is not a virgin.
She is a slut, she just said that to Lester right before sex because usually the guys she seduces seem to like it. It backfired using it on Lester though, but it didn't matter to her either way if they had sex or not.

Angela's intention was to blackmail Lester.
Even with him stopping short of touching her breasts, she still could have blackmailed him - threatening legal action.

Carolyn Burnham was an abused child.
It would explain why she's so obsessed with everything being perfect, why she's so devoted to putting on a Stepford Smiler front and why, whenever it seems to break and she lets her emotions get through, her response is to scream "Stop it!" at herself, usually while giving herself a smack; it's learned behaviour from an abusive parent. In this case, her parent had unreasonably high expectations (obsession with everything being perfect), Carolyn would attempt to meet those expectations no matter how unhappy it would make her (Stepford Smiler) but, when she inevitably fell short, he/she would beat her and then blame her for losing control and crying under the abuse ("Stop it!"). Marrying Lester initially helped her overcome her childhood traumas, but as the marriage soured and they both grew more unhappy with each other she began falling back into old patterns as a coping mechanism.