The estranged partner of a prison guard accused of killing her new lover phoned police on the day she walked out on a “toxic” relationship, worried how he would react, a court heard today.

Former Corrections officer David Benbow, 54, denies murdering Christchurch builder Michael McGrath, who disappeared on May 22, 2017.

His body has never been found – and nor has a murder weapon - despite widespread searches of properties, rivers, waterways and the city dump.

Benbow’s defence team has warned the jury at the High Court in Christchurch of “investigative bias” and “tunnel vision” from police early in its investigations.

The Crown alleges he lured McGrath to his semi-rural lifestyle property in Halswell on Monday, May 22, 2017, and used his .22 semi-automatic rifle, with suppressor and sub-sonic ammunition, to shoot him dead and then dispose of his body, just weeks after learning he was seeing his ex-partner Joanna Green and telling a counsellor he wanted to “annihilate” him.

Today, Green has been giving evidence and explaining what led to her taking their two children and walking out on March 3, 2017.

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

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

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

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, who she had known for the past 17 years and who she always thought highly of, volunteered to help.

“He said, ‘I’d do anything for you ... I’d 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 he 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.

“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.

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.

While the Crown accepts there is no body, no murder weapon, and little forensic evidence in the case, it says there is a strong circumstantial case consisting of many threads that, when taken together, show Benbow is guilty of McGrath’s murder beyond reasonable doubt.

Lead defence counsel Marc Corlett KC earlier said that “within hours” of McGrath’s disappearance, Green had pointed the finger of blame at Benbow “and the police duly obliged”.

But despite teams of police spending thousands of hours investigating “trying to find any evidence they could to fit their theory”, they could not find any, Corlett said.

The trial, before Justice Jonathan Eaton, continues.