This story contains details about Manhunt: The murder of Emily Longley
PREVIEW: When 17-year-old New Zealander Emily Longley was found dead in her boyfriend's bedroom 13 years ago, there was no obvious cause of death.
But why should a young, healthy woman suddenly die in an English south coast town? British police had their suspicions, and Manhunt: The murder of Emily Longley tells that story.
Emily left Auckland in 2009 to attend a college in Bournemouth, Dorset.
Her father, Mark Longley, had misgivings but realised that his strong-willed daughter had made up her mind and there was no point restricting her. She was to stay with her grandparents in Bournemouth.
Emily Longley was murdered aged just 17. Photo: Screenshot
There she met Elliot Turner, a "flash, cash-rich kid who modelled himself on being a gangster".
The night of Emily's death she and Turner argued, violently, as police would later discover.
The documentary plays emergency services audio of Turner's mother calling, the next morning, to say Emily is unresponsive, her necklace tight around her neck.
There are some minor marks on Emily's neck and Turner has a small scratch, but nothing to suggest violence.
Mark Longley's world came "tumbling down" when he was told his daughter might be dead. Photo: Screenshot
Meanwhile in Auckland, Mark receives a shattering phone call.
"We've got a body in the morgue, and we think it's your daughter," he is told.
Longley describes the horror of embarking on the journey to England alongside Emily's sister Hannah, seeing the world go about its business, oblivious to their shared grief.
"I was thinking they should have shut the airport and cancelled the flights.
"Why is no one else sad that my daughter's dead?"
Police unearth a trove of evidence showing Turner is violent, a bully, a narcissist, and had threatened Emily on numerous occasions, once stalking her to a nightclub carrying a concealed hammer.
Senior investigating officer Neil Devoto. Photo: Screenshot
Prior to Emily's death, Turner had made "multiple threats", according to senior investigating officer Neil Devoto.
So convinced are the police that the Turner family is keeping a dark secret that they deploy a "covert product" - essentially, the Turner family home is bugged.
What is recorded confirmed police suspicions.
"He f***ing strangled her," Turner's father Leigh can be heard saying.
Evidence had also been destroyed and it emerges the family were busy colluding to cover Elliot's tracks before calling 999.
"She ruined my life," Elliot Turner says on the covert recordings.
"Their first concern was to concoct a story to get Elliot off," Longley says.
With the circumstantial evidence mounting, the Crown Prosecution Service prepares to file charges of murder against Elliot Turner and perverting the course of justice against his parents, Leigh and Anita.
Throughout his questioning by police and in court, Turner shows not a scrap of remorse, Devoto says.
During the trial, Turner maintains an arrogant swagger, as if the whole thing is a waste of his time, Longley says.
"I thought he was an arrogant prick."
"You don't seem very sad Emily's dead," a lawyer says to Turner during the trial.
"Well, it was a year ago," Turner replies, eliciting a gasp from the gallery.
The documentary shows police seeking further expert evidence on whether a strangulation could occur without significant bruising.
Forensic expert John Payne-James says it is possible to exert severe pressure to the neck without leaving any visible marks.
Emily's sister Hannah Longley. Photo: Screenshot
Turner's claim is that he defended himself after Emily attacked him, grabbed her by the neck briefly, and then pressed down on her as she lay on the bed to stop the attack.
He claims when he woke the next morning, he found Emily lying motionless in the bed beside him.
But friends of Turner's giving evidence at trial bring to light startling new evidence - that Turner had practised choke holds on one friend, using the crook of his elbow, the day before he murdered Emily.
This is enough for the jury. Their verdict is guilty.
His friends coming forward and helping police discover how Turner's domestic abuse escalated is a lesson in calling out male violence early, Longley, who now is a White Ribbon ambassador and campaigner against violence towards women, says.
He and Hannah have rebuilt their lives since he got the news that brought "the walls of my world tumbling down".
"I live with the happy memories of her," he says.
Manhunt: The murder of Emily Longley airs TVNZ 1 at 8pm on 21 October