Focusing on the brutal axe attack which left investigator Daniel Morgan dead in a South London car park back in 1987, the documentary - which took four years to make - digs into why nobody has ever been convicted in the age old case.
And it's reminded people of the harrowing story behind Morgan's death.
In case you need a recap, the victim, Daniel Morgan, was a private investigator who co-owned South London detective agency, Southern Investigations.
After having gone for a drink with a friend, he was found murdered on the floor of the Golden Lion pub in Sydenham, South London, with "two packets of crisps in one hand, his car keys in the other and an axe sticking out of his head".
The Welsh detective tragically left behind a wife and two children after being brutally killed at 36-years-old.
There were no witnesses to his death, and five investigations to find the perpetrator have since collapsed, at a cost of £30 million.
While alive, Morgan investigated drug networks in the area, and is also said to have been looking into police corruption.
As a result of this, his family think that the Met Police are at fault for failing to properly investigate his murder.
One key detail which proves Morgan's death wasn't robbery was the fact that he had £1000 left in his jacket pocket. His watch, however, did get taken.
But what happened next? The truth is we're still none the wiser...
A month after Morgan's murder, six suspects were arrested, and released without charge.
A year later, in 1988, Southern Investigation staff are asked to give evidence during an inquest, and it emerged that Morgan's relationship with the guy he went for a drink with - Jonathan Rees - had deteriorated.
Following this revelation, three men, including Rees, were arrested on suspicion of murder.
But eventually, all were released without charge, and Rees went on to sue the force.
(Interestingly, at this point, Met officer Sid Fillery left his post to join Southern Investigations, where both Morgan and Rees worked...he was later arrested on suspicion of perverting the course of justice in 2008, but his case was dropped).
After Rees sued the force, there was radio silence for a while, until the Met's commissioner, Sir Paul Condon, decided to review the case in 1997.
During the review, anti-corruption officers bugged Southern Investigations and overheard Rees discussing a plan to plant cocaine on an innocent woman as she battled for custody.
He was arrested the following year, and received a seven year jail sentence in 2000.
While many saw this as a breakthrough, the reality was there were still no answers about who killed Morgan, and it stayed that way for two more years.
In 2002, a fourth investigation took place, which involved bugging suspects of the crime. However, the Crown Prosecution decided not to take any action.
Then, in 2005, the fifth investigation occurred, and the Met conceded that their first attempt to unlock the truth was "compromised" by Fillery.
Bugs were planted in the home of Glenn Vian - a key suspect who was the former brother-in-law of Rees, and Daniel Morgan's business parter.
And in 2008, Glenn, Garry Vian and a builder named James Cook were all arrested on the suspicion of Morgan's murder.
But after appearing in the Old Bailey, three witnesses were dismissed, and the cases against all the suspects eventually collapsed.
Detective Chief Superintendent Hamish Campbell said at the time: "This current investigation has identified, ever more clearly, how the initial inquiry failed the family and wider public. It is quite apparent that police corruption was a debilitating factor in that investigation."
Phew, are you still following?!
Now, here's where we are today.
The documentary comes at the perfect time, as in 2013, Home Office called for an independent enquiry, the results of which are expected in the coming months.
Still reeling from what they had been through, Rees, Glenn and Garry Vian, Sid Fillery and James Cook went on to launch a lawsuit against the Met police.
Rees and the Vian won £414,000 on an appeal in 2018, while Fillery was given £25,000 in interim damages, and told that more was coming.
To catch the second episode, set your reminders for Monday 22nd June - or if you want to binge the whole series, it's available to watch on All4.
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