For a three-act plot analysis, put on your screenwriter’s hat. Moviemakers know the formula well: at the end of Act One, the main character is drawn in completely to a conflict. During Act Two, she is farthest away from her goals. At the end of Act Three, the story is resolved.
Act I
Santiago Is the Culprit
In the same sentence that we meet Santiago, we also learn that he is going to die. After a while, you learn what kind of guy he is, what kind of town he lives in, and why he must die. It just so happens that a big wedding happened over the weekend, but the bride was returned to her family for not being a virgin. And guess who she blamed? That's right, poor old Santiago Nasar.
Act II
Is Santiago the Culprit?
After the murder plot is set in motion, the whole town somehow manages to fail at stopping the murder even though everyone knew what was going to happen and even though the murderers didn't even want to kill him in the first place.
The town is left with its own guilt after the murder occurs, and this guilt seems to make things fall apart for almost everybody. Even though there are trials and investigations, the more we learn, the more confusing it all becomes.
Act III
Santiago Is Dead
Normally this is the act where everything is resolved, but you won't find any resolutions here. Everyone just gets old, dies, or kind of forgets about Santiago's murder.
The only resolution we get is the one we've been waiting for from the very first line of the novel. We finally get to see Santiago's actual death with our very own eyes.