In a day of high drama at Manchester Crown Court, the family of Paula Leeson shouted out as the judge intervened to tell the jury that they must find McPherson not guilty of her murder.
Her father, businessman Willy Leeson and his son Neville reacted angrily after Justice Goose cited insufficient evidence for jurors to safely convict the Kiwi, despite previously saying that foul play was "more likely" than an accident, the Daily Mail reported.
Willy Leeson and his wife Betty reportedly broke down in tears, with Leeson shouting: "Oh God, oh God, unbelievable."
The dead woman's brother Neville shouted to the judge: "God Almighty. You are making a big mistake."
The judge told the jury: "I have come to the conclusion that as a matter of law that the evidence in relation to how Paula Leeson came to drown is not sufficiently strong to allow you to reach a proper verdict in relation to the defendant causing it by killing her."
The UK's Crown Prosecution Service reportedly considered appealing against the ruling "at the highest levels" before telling the court there were no reasonable grounds to proceed.
McPherson did not react as he was discharged and told he could go free.
The judge told the court that he understood that the family might struggle to accept the ruling but "the law must be applied equally".
In a statement released by his lawyers, McPherson said: "A tragic accident is what it was and it saddens me, deeply, that the events in question should ever have been seen differently and that I was ever suspected of playing a part in Paula's death."
Prosecutors alleged that McPherson, born Alexander James Lang in Auckland, killed Paula Leeson after taking out a series of insurance policies against the life of the wealthy heiress.
Earlier, the court heard allegations that 47-year-old McPherson killed Leeson while the couple was on a mini-break at a remote cottage in Denmark, before staging her death to appear an accident.
McPherson told police he "froze" when he discovered her lifeless body in a swimming pool.
"I froze. I was in shock, in fear, I was in complete fear and panic, complete panic," he said.
"I just remember getting in the pool to try and get her out of the pool.
"Just seeing her there was horrendous. Horrific."
The court also heard that Leeson "wasn't so keen on water" and neither took swimming costumes on the trip.
The court also heard from Professor Peter Leth, an expert in forensic medicine, who told the court that Leeson had 13 separate injuries on her head and body.
Leth said that while her injuries did not indicate a struggle causing her to go into the pool, violence inflicted by another person could not be ruled out.
However, he noted: "It's possible to drown a person without much struggle, if you are heavier than this person and the person is taken by surprise. That would not leave any marks of any kind."
He agreed with McPherson's lawyer that the injuries could have been caused by Leeson fainting in the pool and later attempts at CPR.
John Ryder QC, asked: "These injuries could be explained by falling and later attempts to recover or resuscitate her?"
Leth replied: "Yes, that's exactly what we have said in our report."
'Tinder for widows'
McPherson's actions after his wife's death also came under scrutiny in the trial.
Days after her death, while McPherson was still in Denmark, he completed an online application to join a support group called Widowed and Young.
Prosecutors said: "His wife had been dead eight days, her body had still yet to be repatriated and laid to rest, and he was joining Widowed and Young."
The court heard that McPherson later described the group as "like Tinder for widows" in a conversation with his personal trainer.
The morning after Leeson's death, McPherson shifted funds from their joint accounts to accounts under his own name.
Prosecutors say he made the transfers to reduce his credit card debt.
Leeson's mother Betty Leeson previously read a statement to the court in which she said it was "strange" that McPherson did not visit his wife's grave for months after her funeral or show emotion at her funeral, the Press Association reported.
Betty Leeson added: "I know he is seeing someone else. Paula was only buried in July. He was seeing an Asian lady by October."
The deceased's brother Neville Leeson told the jury McPherson was "reluctant" to hand over Leeson's iPhone after her death.
When the family eventually got the phone they found selfies of the smiling couple taken on the day she died, despite McPherson telling police that they had been in bed and when he got up he found her lifeless body in the pool.
'Big secret'
The court previously heard that McPherson, originally from Auckland, was keeping secrets from Leeson, whom he married in 2014 in a lavish ceremony at a historic British castle.
Prosecutors alleged that the "big secret" was the insurance policies, but also told the jury that forensic handwriting experts would prove that McPherson forged her will to make himself the beneficiary.
By 2016, McPherson was paying nearly $900 a month in premiums for the life insurance policies. Prosecutors said he never missed a payment despite heavy debts.
The court heard that McPherson, who grew up in Auckland with his parents and two sisters, told his wife that he was an orphan to avoid discussing his past.
He had also trained to be a pilot, keeping his training secret from Leeson by claiming to be working if she called during his flying lessons.
Prosecutor David McLachlan QC previously told the jury: "The prosecution case is, that while at first glance it appeared that her untimely death was an accident, the evidence will show that it was not.
"It was a sinister planned killing and the person responsible for her drowning was none other than her husband Donald McPherson.
"The motive for the drowning was the oldest and simplest one in the book. It was financial.
"He stood to gain a vast fortune by her death. This was something which was not known by the Danish authorities in the immediate aftermath of Paula Leeson's death."
After the judge's ruling, however, the prosecution decided that against an appeal.
The Daily Mail reported Mark Callaghan of the CPS saying: "The CPS function is not to decide whether a person is guilty of a criminal offence, but to make fair, independent and objective assessments about whether it is appropriate to present charges to a court to consider.
"We were satisfied on reviewing the case that there was sufficient evidence to put charges before a jury. However, we have carefully considered the judge's ruling and concluded there are no legal grounds to appeal.
"We appreciate this is very upsetting news for Paula Leeson's family and our thoughts remain with them."
