Liverpool Narcos had Sky Documentaries viewers gripped with its tales of the city's drug trade - and one former undercover cop gained the trust of the gang members who were part of the criminal underworld the show portrays.
In the 1980s, Liverpool was home to some of the biggest dealers, distributors, couriers and debt collectors.
The team behind Liverpool Narcos said they were given "unprecedented access" to some of the biggest players on the scene back then - who warned of the dangers of a life of crime.
But it's not the first time gang members have opened up about the realities of life in Liverpool's criminal underbelly.
Neil Woods is an undercover police officer who spent years infiltrating drugs gangs before writing a book, Drug Wars, that explored Liverpool drug gangs.
He spent 14 years undercover trying to bust major drug operations by befriending dangerous criminals.
In his book, Neil spoke to three men who were involved in Liverpool gangs in the same era as the kingpins featured in Liverpool Narcos.
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Speaking to the ECHO last year, Neil said: "In Liverpool we interviewed three generations of gangsters. The oldest got into it in the 1970s, dealing heroin, and was the right hand man to Curtis Warren.
"The second got into it in the early 1990s - that was when organised crime was becoming more organised, slicker, more corporate and more international.
"The third one was a 16-year-old who escaped county lines after starting dealing when he was 12.
"We asked them all, 'as a young gangster getting into this, how easy was it for you to get access to a gun?'
"The first guy said 'I could have asked the higher ups and they would have spoke to me in detail to ask why I needed a gun and told me not to be stupid'.
"The second one said they had access if they needed them, but you would never give them to young people.
"The 16-year-old said, 'I would need a couple of hours'."
Neil, who is a board member on the Law Enforcement Action Partnership, added: "[This boy] said, 'last time I wanted [a gun] I went to the guy and he said he wouldn't have one in until tomorrow, but he said I could have this hand grenade'.
"He was 15 and that was over territorial beef.
"Merseyside residents should be asking themselves what it will be like when the fourth generation of gangsters are operating."
Neil's undercover police work involved infiltrating drug gangs and earning the trust of their members, in order to try and get closer to the high ranking crime bosses.
But he said his work, and the work of undercover drugs agents, has only served to make criminal gangs smarter, harder and more professional.
Neil never worked undercover on Merseyside - but since leaving the police force he has written extensively on policing tactics used across the world in responding to the war on drugs.
Liverpool Narcos includes both documentary and dramatic reconstructions.
There are three episodes in the series with each focusing on a different drug.
Episode one is about heroin and features Michael Showers, telling the story of how heroin first arrived in Liverpool, creating a new epidemic of drug use while the city was also plunged into mass unemployment
The final episode will air on June 17 and focus on cocaine, with a focus on Stephen Mee in what it terms "the deadliest chapter in Liverpool's drugs war".
You can read more about Drug Wars by Neil Woods and JS Rafaeli on Penguin Books.