Former prison guard David Benbow was yesterday found guilty of killing his childhood friend Mike McGrath. No body or weapon has ever been found. His estranged partner Joanna Green, who had just left Benbow and started seeing McGrath, emerged as a key witness in the high-profile trial and subsequent retrial. Kurt Bayer reports on a love triangle that ended in murder. 

The day she thought “this is it” and finally moved out, Joanna Green rang Mike. Michael McGrath, the ever-dependable family friend, the skilful carpenter who had built their kids’ playhouse and elaborate, sweeping deck. The “lovely, lovely man”, good-looking too, who always cared about her and her children. 

She knew Dave Benbow - her partner of 17 years - wouldn’t take this well. So, she needed help. 

Turning off the CCTV cameras at their lifestyle block on the southern fringes of Christchurch, which Benbow “obsessed” over, she was emotional. She was leaving a “toxic” relationship, one she couldn’t handle anymore, her and the kids’ stuff piled up in the trailer. 

At the end of the driveway, she would joke to McGrath that they should “have a snog”. 

They didn’t. But within weeks, they would. And then, he would vanish. 

She would immediately ring Benbow. 

“What have you done with him?” 

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It would take two years for Benbow to be arrested and charged with McGrath’s murder. 

• David Benbow found guilty of murdering childhood friend
• NZ Herald court reporter: Benbow displayed no emotion following guilty verdict

At the High Court in Christchurch this year, at an initial trial that ended in a hung jury, and then a retrial which ended this week, the Crown alleged that Benbow lured McGrath to his semi-rural lifestyle property in Halswell on Monday, May 22, 2017. It claimed he used his .22 semi-automatic rifle – which has also since disappeared - with suppressor and sub-sonic ammunition, to shoot him dead and then dispose of his body, just weeks after learning he was seeing Green and telling a counsellor he wanted to “annihilate” him. 

Green gave evidence at both trials. 

She explained what led to her taking their two children and walking out on March 3, 2017 – two months before McGrath’s disappearance. 

Christchurch builder Michael Craig McGrath, 49, was last seen at his home in Halswell, Christchurch, in May 2017. 

She claimed Benbow had controlled all of their finances and bank accounts, saying he’d been obsessed with property and money. 

“Our family came second to money,” Green told the court. 

In February 2017, she told Benbow she “can’t do it anymore” and wanted him to move out. He refused. 

So on March 3, 2017, without telling her partner, she organised to leave. 

McGrath, whom she had known for the last 17 years and whom she always thought highly of, volunteered to help. 

“He said, ‘I’d do anything for you bar rob a bank’,” Green told the court. 

On the day she moved out, she made a phone call to police, saying she had “no idea how [Benbow] would react” and wanted to be “covering my bases” and have a record that she was leaving a “toxic relationship”. 

Afterwards, she felt “so relieved” and although nothing had happened between her and McGrath before then, she now felt she could act on her feelings towards him. 

The retrial of David Charles Benbow was held at the High Court in Christchurch. Photo / Pool 

“I’ve always adored him and respected him and now I had a chance of getting the icing on the cake,” she said. 

“He was just such a good man and the opportunity came along. 

“I asked him if he would teach me how to kiss and be touched. I trusted him that much.” 

They discussed whether it would ruin their friendship but McGrath told her: “You could be my soulmate”. 

“He was a good-looking man and very kind. We got on so well. He was a lovely, lovely man. He cared about me and my children and our welfare,” Green said. 

Once together, McGrath would come for tea or bike over once her children were in bed. 

Green didn’t want the kids or Benbow to know she was seeing McGrath. 

“We didn’t want to hurt anyone. I didn’t want to hurt Dave. It was none of his business but he also didn’t need to be hurt by that,” she said. 

But one of her children saw McGrath and her kissing and told Benbow. 

David Benbow leaves the High Court at Christchurch after a hung jury in his first trial in March this year. Photo / George Heard 

He later sent her a handwritten letter where he told her he still loved her and that he was now feeling “very lonely and lost”. 

Benbow apologised for the way things ended and wished her all the best. 

It left Green concerned for him, which she felt was out of character for “a very strong man” that she thought was emotionally unwell. 

She contacted police and raised concerns that Benbow had a firearm and she didn’t want him to hurt himself. 

On May 22, the day that McGrath vanished, teacher aide Green went to work as usual but couldn’t get hold of him. 

She tried ringing him 22 times. 

“I just kept trying and trying and trying to get a hold of him. I was really concerned.” 

Green kept trying the next day without success. 

She waited for the evening and phoned McGrath’s mother Adrienne at 6.38pm to see if he’d showed up for his usual weekly dinner at her place. 

Green rushed around to McGrath’s mother’s house in Halswell, saying, by then she had “red flags”. 

She tried phoning Benbow to see if he knew anything and eventually spoke to him. 

“I said, ‘What have you done with him? Where is he?’” she said. 

“He said, ‘Look, I haven’t done anything’.” 

After going to McGrath’s house with his brother Simon and not finding him home, she phoned police to report him missing. 

The call was replayed to the jury and was heard saying: “I am thinking that he has hurt Mike.” 

After a years-long police investigation, two trials, with dozens of witnesses, the jury agreed. 

- Kurt Bayer is NZME South Island Head of News based in Christchurch. He is a senior journalist who joined the Herald in 2011.