Was Boston a master criminal or was he just a lucky one? As Paradise concludes, Dan and Stephen examine the breaks Boston received that allowed him to escape justice for 38 years.

As the podcast nears its conclusion, fresh information kept hidden in UK Foreign Office files for 40 years delivers yet another twist to this case. Martin Bottomley of the Greater Manchester Police Cold Case Unit gives an unexpected reply to a question Dan hesitates to ask - and it becomes clear this story is far from over. And Boston's public defender, Lexi Nagin, reveals she's an avid listener to the podcast - but hasn't changed her mind about her client.

Vince, Penny and Dan head out to the remote island of Hunting Caye, where Peta and Chris were last seen alive.

They find a near deserted paradise, far removed from any sense of danger. But as they sit and talk, Vince reveals disturbing new details about his father.

Leaving Belize and Vince behind, Penny and Dan go on to the port city of Puerto Barrios in Guatemala in the hope, more than expectation, of finding Chris and Peta’s lost graves.

What they discover at the cemetery leaves them with a creeping sense of unease about the information they'd been given – and the investigation the FBI led.

As Dan heads to Belize, hopes of finding Chris and Peta’s graves in Guatemala fade with new information about the lengths the FBI went to in their attempts to find them. We meet Orlando, Dan’s Belizean fixer, who seems to know everybody in Belize by name as we begin to follow Chris and Peta’s steps. Peta’s letters start to come to life as we trace people and places she mentioned in her letters 40 years before. Very few locals seem to remember Boston – but a visit to the factory Peta write about in her letters leads to a breakthrough in the investigation and Orlando’s experience as a mechanic proves pivotal. Penny joins us in Belize to see some of the places her brother experienced on his travels with Peta in ’78 – before a memorable meeting in Belize City with Vince – the first time they have met. On board a near replica of the Justin B, Vince reconstructs the entire attack. The episode ends with a conclusion to one of the podcast’s biggest questions – but a possibly bigger one remains.

Dan heads to Sandwich in Kent to meet Blaise and Jenny, Peta’s eldest brother and sister-in-law. He hears where Peta got her stoicism from and learns that Blaise was never told that the FBI failed to find the graves.

Back in the States, Detective Amy Crosby hands over files that contain a vital clue to what happened on the Justin B – and raise the possibility of there being two more victims, ‘the Vikings’

Meanwhile, Annie finds the Bombero who pulled the bodies from the water in ’78. What he tells her only leaves us asking more questions - and there’s a troubling inconsistency that clashes with Vince and Russell’s account.

The episode ends with a startling breakthrough that gives us hope we could actually locate the graves of Chris and Peta that the FBI failed to find.

Find out more about the case here: www.bbc.co.uk/paradise

Dan travels to Oxfordshire to meet Penny and her mother, Audrey, who by now is in her nineties. He hears how Audrey and her late husband, Charles, painstakingly tracked down information about Chris and Peta's whereabouts and made appeals on radio and TV.

Back in Greater Manchester, the now retired detective, David Sacks, talks about the investigation he conducted, with the help of Charles Farmer, that centred in on Silas Duane Boston. It's his file, sent to the US in 1979, that Boston's lawyer, Lexi Negin, says contained all the details necessary to frame her client. But were details in that file ever leaked? Dan tracks down the officer in the US who received it, Jim Kelly, to find out.

It's in speaking to Jim Kelly that Dan learns a startling revelation that explains why the case went cold for so long. And it appears Vince and Russell's former step mum, Kathe, may hold the key to closing out Lexi's defence - or maybe there's another way of solving this case.

Find out more about the case here: www.bbc.co.uk/paradise

We visit Boston’s half-sister, Arthene, and hear about his childhood growing up surrounded by criminality. But questions are raised about the stories Boston and Arthene’s mother, Mary Sellers, would tell them and make us question – did she lie to Vince and Russell? Did Boston really kill Mary Lou or was this the warped story of a grandmother who used hurtful lies as a form of emotional control? Before leaving California, Stephen and Dan also meet the third member of the podcast team, US journalist Annie Di Grazia, who starts digging for fresh details on Mary Lou’s disappearance and Chris and Peta’s murders.

A remarkable set of coincidences on both sides of the Atlantic sees Boston arrested after 38 years but with crucial evidence buried, how watertight is this case? Stephen and Dan head to Sacramento to interview Detective Amy Crosby, who led the US cold case investigation of Chris and Peta’s murders. We hear the extraordinary timing of her investigation starting at almost the same time Chris’s sister, Penny Farmer, gets Greater Manchester Police to reopen the case. The evidence stacked against Boston looks compelling but when Stephen and Dan meet prosecutor Matt Segal they find him less than upbeat about how likely a conviction would have been in this case. Surprised by his gloomy assessment they speak to Boston’s public defender, Lexi Negin. It’s the first time anyone’s heard what Boston’s defence was going to be – and what Lexi reveals turns everything on its head.

Find out more about the case here: www.bbc.co.uk/paradise

Vince speaks about his mother’s disappearance in 1968 – and how his own grandmother told him what had happened to her. We learn more about his childhood, growing up with Silas Duane Boston as his only parent. As Stephen and Dan reflect on what Vince has told them they head to CrimeCon in Nashville to investigate potential links to the Golden State Killer case. The conference is buzzing with the news of the arrest of Joseph James DeAngelo, who’s linked by DNA to the crimes. At Crimecon we hear from investigators and victims connected to the GSK case – and there are some interesting reactions to the files we show them. But it’s when we share Vince’s interview with an expert criminologist that doubts start to creep in about his account. Can it really all have happened the way he tells it?

Find out more about the case here: www.bbc.co.uk/paradise

Stephen and Dan head to Savannah, Georgia to meet Vince Boston – son of suspect Silas Duane Boston. Vince (then 13) and his younger brother, Russell (12), were on board the ‘Justin B’ with their dad, when they met Chris and Peta in June 1978. Through Vince’s words and Peta’s letters we hear about their happy first few days as they sail south from Belize. But as Peta’s writings grow more troubled, Vince details how his father’s temperament grew more and more menacing. Vince’s account turns into a horror story as he recounts how he was made to stand guard over Peta the night before she and Chris were killed. Vince tells Stephen every detail of the unfolding plot that leads to their drowning. The question is – what had his father done to him to render him so silent in the face of such terror?

Find out more about the case here: www.bbc.co.uk/paradise

In 1978 the bodies of a young male and female couple were found hogtied and drowned off Guatemala’s Caribbean coast. Nine months later they were identified as British graduates Peta Frampton and Chris Farmer.

Police in Manchester, England quickly focused in on an American called Silas Duane Boston who had offered to sail Chris and Peta from Belize to Costa Rica on board his boat, the Justin B.

Boston’s boat never reached Costa Rica and he fled back to California with his two young sons soon after the murders. So why did it take 38 years to arrest him – and how could he maintain his innocence when both his boys were telling the FBI they saw him do it?

As 5 live journalist Dan Maudsley and BBC presenter Stephen Nolan investigate, this open and shut case only becomes more complicated.

Find out more about the case here: www.bbc.co.uk/paradise