In 2011, Longley flew from New Zealand to the UK to hear at a trial how his daughter, who was studying there, had been dating Elliot Turner - someone who was threatening, openly aggressive with her on nights out, and spoke often of how he would kill her.
And then he did, by strangulation.
The subsequent bugging of his house revealed his parents had tried to help him cover up the murder.
"It's had a huge impact on me. I wouldn't be trying to raise awareness around domestic violence and sexual violence if Emily hadn't died. I would've been one of the millions of people who think it's not really a problem," Longley said.