The secretary-general of Interpol, Ronald K Noble, may have thought he had little to fear from the Belarusian mother whose son was shot dead after he and a friend confessed to planting a bomb that killed 15 people on the Minsk underground system last year.
But Lyuba Kovaleva is fighting a campaign that has raised grave questions about Mr Noble's judgment, and is lending weight to claims that the Belarusian secret police, the KGB, planted the device, rigged a show trial and tortured confessions out of the two suspects.
The tale begins two days after the metro bombing in April last year. President Alexander Lukashenko – routinely called the "last dictator in Europe" – announced on television that, thanks to a KGB investigation, two men had confessed to the crime. He said they would face "the most extreme punishment". The men were Ms Kovaleva's son, Vlad Kovalev, and his flatmate – the alleged bomber – Dima Konovalov.
A month later, Mr Noble, an American, arrived in Minsk and held a press conference where he is said to have compared the metro attack to the bombing of London's transport network on 7 July 2005. He called Mr Konovalov "a terrorist" and praised "the high professionalism" of the Belarusian criminal investigation for solving the case "so quickly".
The trial of the two suspects began four months later. They were found guilty in November and in March this year both were executed with a bullet to the back of the head. Mr Noble has been accused by opposition figures in Belarus of abandoning the presumption of innocence until proven guilty, leaving himself open to the charge of being Mr Lukashenko's "useful idiot" – criticisms Interpol hotly disputes.
In Vitebsk, three hours east of Minsk, I met Ms Kovaleva. A slight, frail woman racked with grief, she said she was often watched by the KGB but that the coast was clear that day.
"The court has not a single piece of proof of guilt, not only of my son – who was dragged into this – but also of Dima Konovalov, apart from Dima's confession, which he gave under torture," she said in response to the official version of events – that the men had a fair trial. "They were beaten to such an extent that when we were shown the video recording of Dima being interrogated, he could barely speak. He could barely sit."
Opposition activists both inside and outside Belarus have claimed they were tortured at KGB headquarters in central Minsk.
They say that in December 2010, after a bitterly disputed election, victims were forced to strip naked and stand in stress positions while masked guards swished electric batons. Icicles hung from open windows and the temperature outside was minus 20°C.
As part of my investigation, I went to a freezer warehouse in North London to experience it myself. I stripped off and stood in the Amerikanka stress torture position for as long as I could bear. Opposition activists say they had to endure 40 minutes. I lasted 40 seconds.
In the case of the Minsk metro bombing, Ms Kovoleva said her son and his friend never stood a chance of a fair trial. "On 13 April at 9am on the radio, I heard Lukashenko's announcement that the culprits had already been arrested, and that they would receive the harshest punishment – they would be shot," she said. "He said the boys had been interrogated and by 5am they had already confessed."
Mr Noble was not available for comment. A spokesman for Interpol denied that the presumption of innocence was breached and disputed my conclusions about the evidence.
John Sweeney's report Torture In The 21st Century, will be broadcast on BBC Radio 4 at 11am today and on BBC2's Newsnight programme at 10.30pm. His e-book, Big Daddy: Lukashenka, Tyrant of Belarus is published by Silvertail Books