This is what Agatha Christie's stories and their adaptations so good. The murder usually only happens at the end of the first act or halfway through the novel, where we get a good look at how the victim interacted with the suspects to get an understanding as to why they would want the victim dead.

A great example of this is the film version of Evil Under The Sun, where Poirot is asked to go in holiday to help confront a suspected jewel thief and along the way, we see the victim interacting with the other characters and it's made clear that nearly everyone has a reason to want her dead. She's only murdered halfway through the film, with the first half revealing;

• She jilted her ex-fiancé to go off and marry another man, stealing a million-dollar diamond from him in the process;
• She's secretly brought the man she's cheating on her newlywed husband with on her honeymoon;
• She's rubbing it into the face of her affair's own wife;
• She's a truly wicked stepmother;
• She's screwed her publicist out of thousands by refusing to sign off on the release of a book;
• She bailed on a major Broadway production and got it cancelled three weeks into a six-month contract, leaving her bosses broke;
• She may have ruined a rival actress' career and is currently married to the man the other actress is in love with.

Edit: Also, fun fact - the victim in that film, Arlena Marshall, was played by Diana Rigg AKA Olenna Tyrell in Game of Thrones.