What Makes a Killer is a true crime series organised into seasons, and its episode titles read like the index of a case file: Bobby Joe Long, Christopher Hightower, Vincent Tabak, Daniel Lee Siebert, Stuart Hazell, The Hillside Stranglers. Each episode belongs to one case. That lets the show range across time and place. Its cases are set in Los Angeles in 1977, Tampa in 1984, Guilford, Connecticut in 1991, Bristol on Christmas Day 2010 and South London in 2012. Most episodes set the scene exactly that way, with a date and a location straight after a warning about graphic content. Then the investigation takes over. In the Hillside Stranglers case, detectives took the lack of drag marks on a body as a sign that two men were at work, and a fibre on a victim's eyelid showed she had been blindfolded. In the Daniel Lee Siebert case, investigators describe finding a campsite up an embankment from a car, then matching fingerprints that confirmed they had their man. The Vincent Tabak episode rebuilds Joanna Yates's last evening from pub CCTV and from a couple at a nearby party who heard two screams. Investigators speak in their own voices here, not only through narration. The Bobby Joe Long episode also brings in author Anna Flower and criminologist Dr. Elizabeth Yardley. The question in the show's name comes through in how the killers are drawn. Long is described through his divorce and a ferocious hatred of women, and Hightower as a pathological liar. One killer is described keeping up a 'gentle giant' facade that convinced his own family he was innocent. Trust keeps coming up. Tabak was a neighbour whom Joanna Yates probably let in. Hightower, a family friend, phoned a school and then a YMCA pretending to be a girl's father so he could collect an eight-year-old. In the Stuart Hazell episode, the last person to see 12-year-old Tia Sharp was the man she called Granddad. The narration leans dramatic, with lines like 'a fresh hunting ground', while the interview voices are plainer and rawer. The Long episode also includes a survivor, a 17-year-old named Lisa. Several episodes end by turning toward the next case in the season, so a run of them carries some momentum. Jennifer Notoso introduces the series as its host in the Stuart Hazell episode. For a first listen, 'S5 Ep9: The Hillside Stranglers' is a good showcase for the detective work, and 'S5 Ep11: Vincent Tabak' shows how the show rebuilds a victim's last hours from small pieces of evidence. The material is heavy throughout, with sexual violence, murder and harm to children at the core of these cases.