The Pembrokeshire Murders, ITV review ★★★★★

The trouble with true-crime procedurals is that they’re always at risk of becoming exactly that: procedural. ITV has broadcast many excellent examples such as A Confession, White House Farm and Des, but all of them have an extra layer, an intensity, that reaches beyond the usual. The Pembrokeshire Murders is its latest true-crime offering of event TV, airing each night from Monday to Wednesday. But the three-part drama never stands on that upper level of intrigue, only grazes it.

The series is based on the case of Welsh serial killer John William Cooper, convicted of murdering four people in the 80s as well as rape and sexual assault in 1996. But here’s the twist: he appeared on the cheesy darts game show Bullseye between the murders. It was a revelation that proved vital during the investigation by DSI Steve Wilkins from 2006 to 2011.

DSI Steve Wilkins (Luke Evans) with DI Ella Richards (Alexandria Riley). Photo: ITV

Steve (a naturalistically muted performance by Luke Evans) cleans his mugs and folds his towels (look how meticulous he is!). He attempts to rebuild his relationship with his son after a divorce. And he has an embarrassing plaque on the wall reminding him of his job description. Oh, and, if you haven’t guessed, he’s the type of detective who gets things done and thinks in greater detail than everyone else.

He’s determined to find the evidence against Cooper, who’s about to be released from a burglary sentence. The standard steps are made: the classic montage of photos, maps, and pins on whiteboards – set up in a secret office somewhere. All while Cooper (a seething, gruff and grey Keith Allen) is idling away his remaining prison time, playing darts in his cell (like Bullseye… get it?) and frightening his anxious wife Pat (Caroline Berry) during visiting hours.

Oliver Ryan plays Andrew Cooper, John Cooper's son. Photo: ITV

The series is saved from its tedium via Andrew (Oliver Ryan), Cooper’s son, who elevates the otherwise predictable plot. He suffers the most, burdened by his past growing up with Cooper as a father. He lives in squalid surroundings, living with a disability and clutching his walking stick tight – spending ages on the phone claiming benefits.

The small moments of Andrew without the police are the most moving. The series' closing scene stirs as he has the deserved final word. Once the inevitable courtroom scenes begin, it’s him as much as Cooper’s rape survivors who become memorable assets – not least because of the affecting trauma in their performances.

The final episode has a lasting impact, to the point where you wonder why the writer, Nick Stevens, bothered with three. It sees more of John Cooper in the interrogation room. Director Marc Evans and cinematographer Baz Irvine capture a gripping picture of a narcissistic psychopath under pressure. At one point, his face reaches forward from uncomfortably shallow focus, like he’s coming out of the screen at you.

But Cooper's character doesn’t attract much curiosity: he’s too obviously a psycho. That may well have been the case in reality, but there’s no absorbing nuance – he’s just horrible. Dennis Nilsen and Christopher Halliwell had a scary calm about them; Cooper just adheres to his stereotype.

The Pembrokeshire Murders airs Monday 11 January to Wednesday 13 January at 9pm on ITV