The Pembrokeshire Murders saw the action pick up during the second episode as the investigation intensified into John Cooper's role in the 1980s murders - and it included classic TV footage from the decade.
Cooper famously appeared on the ITV quiz show Bullseye in 1989, the episode recorded just a month before he viciously killed Peter and Gwenda Dixon on the Pembrokeshire Coastal Path.
For the second episode of the ITV drama the original Bullseye footage was used with actor Keith Allen's face superimposed onto that of Cooper.
The TV footage played a vital part in Operation Ottowa's (the name of the investigation) efforts in identifying Cooper as the suspect seen using the Dixon's card at a cashpoint back in 1989.
But viewers of the drama who didn't know about the case beforehand, were amazed by the Bullseye connection.
One Twitter user wrote: "Can’t believe they caught a serial killer from an episode of Bullseye it’s completely blown my mind."
And while Allen's performance was getting a lot of plaudits for his chilling portrayal of Cooper, some viewers didn't like the super-imposing of his face onto the Bullseye footage.
One Tweeter thought the use of the actual footage was good, but unsure about the CGI face.
Another viewer wrote on Twitter; "You could see they had put Keith Allen’s eyes into John coopers [sic] face and it looked silly,such a shame because they used all John coopers original pictures and some videos then done that."
