From the 1980s to the late 1990s, a series of murders and sexual assaults took place in the southwest of Wales, an idyllic area known for its walking trails and scenic coastline. Police manhunts failed to expose the killer.
In 2006, detective Steve Wilkins reopened the case. The three-part true-crime miniseries The Pembrokeshire Murders details the efforts of his team's cold-case investigation.
Actor Luke Evans, speaking to The Straits Times on a Zoom call from Miami, Florida, talked about what it took to play Wilkins, a low-key, almost drably normal person.
He is an anomaly in a television landscape filled with fictional detectives damaged by addiction, trauma or a mental handicap.
Evans, 41, says: "I discovered with my research, and in meeting Steve, is that people in that profession are very contained, very methodical.
"As a detective, the last thing you want in an interrogation, or when you are arresting somebody, is to be overly emotional or aggressive."
The Welsh actor has played his share of larger-than-life characters, from villain Owen Shaw in the Fast And Furious film franchise (2001 to present) to the dragon-slaying Bard in The Hobbit fantasy films (2012 to 2014).
Not much embellishment was needed to tell the story of Operation Ottawa, as the exercise to catch the killer was called.
"The hours they invested to find tiny pieces of information and how luck and timing played a part - it blew my mind," says Evans. "It attracted me to tell the story. This is about finding the depth and nuance in his character, which is what I hopefully have achieved."
One detail he wanted to learn from meeting the real Wilkins was what it takes to be a cold-case investigator, a breed of detective whose brief is to succeed where others have failed.
A trait of such a person, says Evans, is the ability to inspire hope in a team while knowing that there is every chance their efforts could be for nothing.
"To open a cold case, you're going to look at evidence that has been looked at many times before. That's a daunting task for any investigative team."
Another operational fact that piqued Evans's interest was how Wilkin's investigators isolated themselves from other detectives, especially ones who had worked the same cases previously.
"The cold-case investigators actually took a separate office, away from the influence of anybody else, so that they would be able to do their investigation as if it was a new one.
"That fascinated me because I thought it sounded so much like a movie," he says.
Because the crimes are relatively recent, Evans says it was important that the story be told without sensationalising it.
"When you're playing a character in a true story, you know it will affect many people, including people that were directly affected by these crimes. You have an even bigger sense of responsibility to play it real, to live the journey taken by the real human being."
The Pembrokeshire Murders premieres Friday (Feb 26). Available on BBC First (StarHub Channel 502) and BBC Player.