Filmmakers are often inspired by real events. Sometime they merely use them as a backdrop for their fictional story, à la “Titanic.” Other times the real events are the story, as in biopics like “Walk the Line.” But to make a movie based on unsolved murders from some 20 years ago is a bit unusual. By definition, with an unsolved crime, you’ve given away the ending, or non-ending, as the case may be. Writer and director Bong Joon-ho took such a gamble, and it paid off quite nicely with his masterful 2003 film, “Memories of Murder.”

Based on a series of gruesome serial killings that started in 1986 in rural South Korea, “Memories of Murder” became one of the country’s top-grossing films of 2003, going on to win that year’s Grand Bell Award (the Korean equivalent of the Best Picture Oscar). It stars Song Kang-ho (from “Shiri” and a number of Park Chan-wook’s films, including “Joint Security Area” and “Sympathy for Mr. Vengeance”) as Park, the blustery detective in charge of a particularly brutal murder case. His rough, macho tactics may have worked on the petty activities of the local village in the past, but when faced with the magnitude of these horrific crimes, it is clear he is in over his head.

Of course he’s none too happy when Seo, a more experienced detective from Seoul (played by popular stage actor Kim Sang-kyung), joins in the investigation. Seo dismisses detective Park’s brutal techniques, such as beating false confessions out of suspects, as counterproductive, especially as the murders keep mounting. Seo’s methodical, more scientific approach relies on gathering and analyzing evidence, such as noting that all the murders occur on rainy nights. When a female police officer also discovers another unusual coincidence, even Park realizes that they have some legitimate clues to help them solve the case.

But finding the true killer proves difficult. Their best chance comes with a DNA sample found at a crime scene. But DNA analysis is still a new technique in the mid-’80s, especially in rural Korea, so Park and Seo are obliged to send their evidence to the United States to be properly tested. When the results come back negative, they are both crushed, and their roles are reversed, with Seo on the verge of shooting a suspect in order to come to some sort of sense of justice. A brief, but powerful epilogue, set 17 years later, reveals how haunted the detectives have become by the unsolved cases.

By leaving the film open-ended, some could criticize Bong’s film as being unsatisfying and incomplete. Nonetheless, the film’s gorgeous cinematography is unassailable. The rustic farmlands, a towering factory and the shadowy police station all lend brooding ambience to the story. The subtle references to South Korea’s social climate of the ’80s — from civil unrest (backup police officers are often not available, as they are busy suppressing political protests) to sexism (despite discovering a crucial clue, the female officer is mainly asked to make coffee for the other cops) to the rampant police brutality — allow the director to create a definite sense of place and time. And despite the unresolved nature of the story, Bong does leave some tantalizing clues for the viewer to ponder over.