The Essex lorry incident in October 2019 which claimed the lives of nearly 40 Vietnamese migrants was one of the Uk’s most shocking crimes.
The deaths of the migrants were discovered when a lorry driver opened the rear doors of his trailer and discovered their lifeless bodies - it was apparent from the outset they had tried to break free.
BBC Two will explore the investigation which got underway in the immediate aftermath and how it uncovered a multi-million-pound smuggling ring.
Here is what you need to know about the case, ahead of the documentary.
When is ‘Hunting the Essex Lorry killers’ on TV?
The documentary, following the case of the Essex lorry killers, will air on 13 October at 9pm on BBC Two.
It will be available on iPlayer shortly afterwards.
What is the documentary about?
Hunting the Essex Lorry Killers follows the police investigation into the 23 October 2019 incident where a Northern Irish smuggling gang accidentally killed 39 Vietnamese migrants.
The bodies of the dead were found by lorry driver Mo Robinson, originally from County Armagh, when he collected the refrigerated-container lorry from Grays in Thurrock, Essex.
The documentary will show how detectives unveiled a multi-million-pound international smuggling ring, with its roots in a seemingly innocuous haulage business in the heart of Northern Ireland.
BBC Two gained exclusive access to Essex Police and the officers on the case, as it tells how evidence as pieced together and witness testimony proved a gang were behind the smuggling case.
Filmmakers also traveled to Vietnam to meet the families of some of those who died in the back of the lorry, hearing their heartbreaking stories of losing loved ones on the false promise of a new life in the UK.
How did the Vietnamese migrants die?
The smuggling of the migrants was carefully coordinated and each stage planned by the gang, but the 39 people were supposed to reach Britain alive.
The victims paid large sums of money to be taken from France to the UK, the migrants had paid large sums of money and made their own way as far as France or Belgium and then boarded the trailer.
Enroute to the UK, the container also visited Zeebruge in Belgium on a freight ferry to the town of Purfleet before reaching its destination.
GPS has shown it also visited Dunkirk and Lille in France and Bruges in Belgium beforehand.
Judge Mr Justice Sweeney said of the case: "I have no doubt that the conspiracy was a sophisticated, long-running and profitable one to smuggle mainly Vietnamese people across the channel."
He said on the fatal trip the temperature had been rising along with the carbon dioxide levels throughout, hitting 40C (104F) while the container was at sea on 22 October 2019.
"There were desperate attempts to contact the outside world by phone and to break through the roof of the container," the judge said.
"All were to no avail and, before the ship reached Purfleet, [the victims] all died in what must have been an excruciatingly painful death."
The victims had used a metal pole to try to punch through the roof but only managed to dent the interior and some had stripped to their underwear in a bid to survive the sweltering heat.
Some made contact with their families as they realised they were locked inside and slowly losing access to oxygen.
"I can’t breathe," one man said on a voicemail to his family, "I want to come back to my family. Have a good life."
Justice Sweeney added: "The willingness of the victims to try and enter the country illegally provides no excuse for what happened to them."
The lorry carried 28 men, eight women and three boys - the youngest boys aged just 15.
The father of Nguyen Huy Tung, one of two 15-year-olds in the container, learned of his son’s death on social media.
Another victim’s father claimed his son must have been tricked, as he paid the money in the belief he was to receive “VIP treatment”, entering the UK in a cab and not the back of a lorry.
It was later confirmed by Essex Police that the deaths were as a result of a combination of hypoxia and hyperthermia, as the refrigerated truck they were in could be kept airtight.
Who was convicted for the Essex lorry deaths?
Mo Robinson, 26, the lorry driver who discovered the bodies, was convicted of manslaughter and sentenced to 13 years in prison - he also admitted to money laundering and people smuggling.
He spent 20 minutes on the phone to his aliases before phoning 999 when he discovered the bodies.
Ronan Hughes, 41, and Gheorghe Nica, 43, played "leading roles" in the smuggling conspiracy - Hughes owned the trailers used and Nica arranged for the migrants’ transport once they reached the UK.
The pair had "recruited and paid the drivers whose job it was to collect the migrants when they reached the drop-off site in this country and to drive them to the safe house(s) where they were to be held until payment,” argued Mr Judge Sweeney.
He added at the top of the conspiracy was a Vietnamese man called "Fong", who was based in London.
Hughes, of Tyholland, County Monaghan, and Nica were sentenced to 27 and 20 years retrospectively in prison.
Eamonn Harrison, of County Down, who delivered the trailer to Zeebrugge was sentenced to 18 years. He claimed he did not know there were people in the trailer when he collected it.
Three other members of the people-smuggling gang were also sentenced for conspiracy to facilitate unlawful immigration.
Christopher Kennedy, 24, from County Armagh, was jailed for seven years; Valentin Calota, 38, of Birmingham, for four-and-a-half years; and Alexandru-Ovidiu Hanga, 28, of Hobart Road, Tilbury, Essex, was given a three-year sentence.