"In the days leading up to the victim's death he became more and more fixated on her, and fixing their relationship."
After Scantee ended the relationship, she began making plans to move back to Romania, where she was from.
In the week leading up to her death, she spent small amounts of time with McConachie, but remained adamant she no longer wanted to be in a relationship with him.
On the night of the murder, McConachie drove to the house in Paraparaumu Beach where Scantee was staying and asked her to come and speak with him in his car.
Irina Scantee was making plans to return home to Romania when McConachie murdered her. Photo / Supplied
Scantee, still dressed in her pyjamas, slippers and dressing gown and not carrying her phone or wallet went to speak with McConachie, who ended up driving her away from the property.
"Either during the journey or at the time of parking, the defendant began to strangle the victim," the summary said.
Scantee managed to get out of the car and tried to get away from McConachie, who was following her.
Several witnesses approached as Scantee told them "help, he is trying to kill me" and "he has strangled me". They could see red marks around her neck as she spoke.
McConachie at first tried to claim Scantee had been attacking him, before retreating to his car and grabbing a box cutting knife.
He returned to the group, grabbed Scantee in a headlock and slashed her throat with the box cutter, the summary said.
When Scantee fell to the ground, McConachie continued cutting at her throat, "causing her almost immediate death".
He then drove away from the scene, sending text messages to friends and family announcing he had killed Scantee.
McConachie drove for about 5km before he tried to harm himself, after which he called police and told them what he had done.
Crown prosecutor Grant Burston said the killing was driven by McConachie's jealousy and anger, and was carried out in a "brutally determined way".
He also noted McConachie told report writers he felt he could be at risk of offending in a similar way in the future.
Brian McConachie slashed his ex girlfriend's throat in the weeks after their break up. Photo / Supplied
He had a history of being in relationships and exhibiting "concerning behaviours" at the end of those relationships.
Defence lawyer Val Nisbet said McConachie had limited cognitive ability.
"He still struggles to comprehend how and why he could have done such a thing."
He argued a sentence of life imprisonment would be manifestly unjust due to McConachie's mental health issues making prison a particularly difficult place for him.
Justice Simon France said McConachie was hospitalised after the break up as he struggled to cope with the end of the relationship.
But just days after he was released from hospital, he took Scantee's life.
Justice France outlined an extensive history of mental health incidents McConachie had experienced, many revolving around relationship issues. He said he had never been diagnosed with a major mental illness.
He labelled the killing a "premeditated, brutal murder carried out in full public view".
"He plainly had ideas of suicide, but he decided he would also kill the victim."
He sentenced him to life imprisonment, with a minimum non-parole period of 10 years.
