Det Sgt Darren Davies says messages MacPhail sent to Holly clearly showed coercive behaviour.
“He would talk about the break-up and how he’d harm himself if she didn’t speak to him,” he says. “It is a fairly common tactic of perpetrators to get people back on side as a sympathy element.
“For a 15-year-old girl to hear that can’t have been easy and Holly didn’t understand what that was.”
The prevalence of mobile phones and social media can make teenage relationships “more intense”, Det Sgt Davies adds.
“The big thing I have taken away from the case itself is the relationship those two had at the age they were,” he says.
“You realise just how much contact kids have with each other and those relationships are far more intense and involved than I think a lot of adults probably appreciate.”
Society has a responsibility to help children navigate the complicated world of relationships, he says, adding: “Just talk to them and promote healthy relationships and boundaries, show them what’s healthy and what’s not.”
A Home Office spokesperson said the government’s “thoughts remain with Holly Newton’s loved ones after her horrific murder”.
They said there was a “clear mission” to halve violence against women and girls within a decade.
“As part of this, we will be looking closely at how we can intervene at the earliest opportunity to protect girls when children present such harmful behaviours,” the spokesperson added.
