Brendon McCullum says the inexorable pressure of testifying against former teammate Chris Cairns ushered his premature retirement from cricket.
Former New Zealand captain McCullum has revealed the toll that being a witness in the 2015 perjury trial of allrounder Cairns took on him in his newly released book "Declared".
Cairns was acquitted of the charges, related to alleged match fixing.
That finding came near the end New Zealand's tour of Australia, during which McCullum made a decision to accelerate retirement later that summer.
He had originally planned to play at the subsequent World Twenty20 in India but found his motivation had waned considerably following a heavily scrutinised role as a witness at Southwark Crown Court in London.
"It's impossible to ignore the fallout from the trial completely, and it's been chipping away at me like Chinese water torture right through the Australian tour," McCullum wrote.
McCullum goes into further detail around the trial, expressing surprise he proved to be the key prosecution witness.
He lamented how the trial was portrayed in the media as a battle between himself and Cairns - a former friend and player he first regarded as a hero.
He admits their relationship is now irreparably damaged.
McCullum was one of three key Crown witness against Cairns, along with disgraced former cricketer Lou Vincent and Vincent's ex-wife Eleanor Riley.
McCullum expressed concern at the summation of Justice Nigel Sweeney, who instructed the jury to be sure of the evidence of at least two witnesses before they could convict Cairns.
Vincent was discredited by the defence as a confessed match-fixer while Riley's evidence was about alleged confessions from Cairns on a drunken night out.
McCullum doesn't understand why his evidence alone couldn't be enough to bring about a conviction.
He says he has wondered often since if he made the right decision to put himself through the stress of testifying - something he didn't have to do.
"I was prepared to stand up, even under pressure and under fire from various quarters, and do what I thought was morally right at the time," he wrote.