The case of Ruth Ellis caused shock waves through British society in 1955 and still reverberates today. Found guilty of murdering her lover, David Blakely, she was the last woman to be hanged in Britain, with many observers at the time on both sides of the fence stunned that the Home Secretary, Lloyd George, refused to commute her sentence. What first appeared to be an open and shut case of a woman gunning down the man who was set to abandon her, reveals layer upon layer of dubiety, sleaze, and scandal, and filmmaker Gillian Pachter (a documentarian who has covered US murders in the past) aims to uncover yet more details to make us shudder at the injustice of it all.

Over the course of three hours, she explores the criminal investigation, the court case, and the subsequent calls for Ellis to be saved from the gallows, and finds everything from police incompetency to a possible state conspiracy which sealed her fate. Ellis's main crime was being a working-class woman (a model and waitress) who fell for a posh and brutal man who once raced his fast car on the same track as Stirling Moss.

The question of whether Ellis fired the gun is never in any doubt. But the circumstances that led to the slaying would, just a few short years later, have led to a conviction for manslaughter via a defence of diminished responsibility: after a lengthy period of physical abuse at Blakely's hands, Ellis suffered a miscarriage a fortnight prior to the killing when he punched her in the stomach.

Pachter's trigger for this re-examination is the 1982 suicide of Ellis's deeply troubled son, Andre, who as a ten-year-old witnessed events and overheard conversations that could have saved his mother but who was never questioned by police or social services about the crime. The case is compelling and disturbing, but the telling of it is a little jarring at times. The deadpan Pachter puts herself front and centre of the action with lots (and lots) of shots of her walking around to meet interviewees and pouring over reports of the case in dimly lit library spaces, while her sympathy with Ellis is clear: it could be a coincidence, but at one point we cut away from Pachter wearing a stripy top to an image of Ellis in almost identical knitwear.

But more irritating is the constant use of the same set of photographs of the drama's players, and old black and white noir movies which punctuate the story: at first this makes you think you're watching an Adam Curtis film, but ultimately it gives this serious subject an air of slapstick that is wholly inappropriate. The evidence and interviewees that Pachter uncovers are compelling enough without resorting to distracting add-ons.

Episodes watched: all three.

The Ruth Ellis Files: A Very British Crime Story is on BBC Four, Tue 13–Thu 15 Mar, 9pm.