The penultimate episode of the BBC series, which aired on Sunday night saw AC-12 communicating with the Spanish police as they raided the house believed to be inhabited by Thurwell.
Upon entering the property, we saw a very pixelated view from the body cam footage of what appeared to be the corpses of one female and one male laying on a bed.
The Spanish police officer, who was talking to AC-12 via video link, declared Thurwell as the dead male in the property.
Watch: James Nesbitt discusses Line of Duty role
During DCI Joanne Davidson’s (Kelly MacDonald) interview, we learn that Thurwell was working on the Lawrence Christopher case in 2003, in which a young Black man died in police custody.
Gail Vella, the journalist whose murder this series is focused around, was looking into this case, and we are led to believe that her motivations surrounding exposing the case and the police corruption that ensued during it, was the reason for her subsequent murder.
Thurwell retired from the police force in 2005 and, aside from being briefly questioned by AC-12 in 2015 over Sands View, he disappeared to Spain when former Chief Superintendent Patrick Fairbank (George Costigan) was convicted.
AC-12 are suspicious of his OCG links, hence the importance of the house raid in Sunday’s episode.
However, viewers were less than convinced that Thurwell could accurately be pronounced as dead, with one even suggesting that that police officer communicating with AC-12 on the video link shared a vague resemblance to Thurwell himself.
Adding more fuel to the fire, Phillip Schofield and Holly Willoughby "trod the line of duty" very carefully on Tuesday’s This Morning as they teased viewers with the announcement that a very special Line of Duty guest would be appearing on the show on Monday.
“The country is gripped by Line Of Duty we have – and all I'm allowed to say is – on Monday's show a very exciting guest, pertaining to that show, on Monday.”
“I'm treading the line of what we were told we were allowed to say this morning and I think I've gone right down the middle of it.”
Known for their on-air blunders, Willoughby said that she was relieved she wasn’t the one delivering the news to viewers as she, “definitely would have messed that up”.
It's a speculative leap to suggest that This Morning couldn't reveal its guest because it's James Nesbitt, but it's one we're willing to make.
Also during Sunday's episode of the BBC drama, we saw Davidson’s distressing reaction to finding out that her real father was in fact Tommy Hunter, whom she believed to be her uncle.
When asked by DI Steve Arnott (Martin Compston), whom she believed was her father, she answered: “No comment.”
However, one viewer speculated that it could in fact be Thurwell who Davidson believed was her real father.
Watch: Martin Compston shares Line of Duty pranks with co-star Vicky McClure