Crying with grief and anger, Fatima Khan stormed forward and shouted: "You killed my son!"
As Syria's warring sides held a sixth day of UN-brokered peace talks in Geneva, the mother of a British doctor who died in the custody of President Bashar al-Assad's regime confronted his aides Thursday.
Syria says that Abbas Khan, 32, was found hanging in a prison cell on December 16, 2013, and that he committed suicide.
His relatives are adamant he was murdered by his captors.
Having travelled from Britain to Switzerland and obtained a visitor's pass to the UN's European offices -- where the talks were under way behind closed doors -- Fatima Khan waited for hours for delegates to emerge and speak to journalists in the garden.
She seized her chance when top Assad aide Buthaina Shaaban came out for the cameras.
Shaaban appeared caught off guard, asking who the distraught woman was.
"The doctor's mother," responded a man in the crowd.
Shaaban did not comment on Khan's charge, simply murmuring: "Let's get away from here."
Khan was ushered away by UN security guards, as reporters from across Syria's divide traded barbs.
A pro-regime journalist told her to get lost, sparking an irony-laced reaction from an anti-regime rival: "In Syria you lay down the law, but not here! So the doctor killed himself? Are you sure you didn't kill him?"
Khan, the father of two children, was detained in November 2012 in the war-ravaged city of Aleppo just 48 hours after entering Syria from Turkey without a visa to help treat victims of hospital bombings.
"For five months he was in a civil prison, and for eight months he was in a torture prison, where they are torturing and killing thousands of people," his mother told AFP Thursday.
She received a Syrian visa and visited him behind bars in July 2013.
"When I saw him in prison, he told me, 'Mummy, look, I'm a doctor, I'm a humanitarian aid worker, and look what they did to me. So imagine what they're doing to their own people,'" she said.
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Despite saying the world should be rid of the Assad regime, Khan denied she had become an opposition tool.
"I'm not representing the opposition, I'm representing half a million mothers inside Syria," she told AFP.
'Caught with a medical kit, not a weapon'
The Syrian conflict erupted in March 2011 after a crackdown on pro-democracy protests and morphed into a war that has killed more than 130,000 people and driven millions from their homes.
The regime spotlights the role of hardline Islamists from Syria and abroad that are fighting it, and slaps the "terrorist" label on the entire opposition.
The opposition Free Syrian Army, which is itself fighting the jihadists as well as Assad, says that is an excuse for regime brutality.
Khan had been due at a terrorism court the day after his body was found. His mother rejected suggestions that he had an ulterior motive for entering Syria.
"He was not caught with a weapon, he was caught with a medical kit," she said, adding that he had a return flight booked from Turkey on November 24, 2012.
"If they don't understand what a doctor's profession is, if they don't know what a humanitarian aid worker is, then they should not be in power."
Khan worked at London's Royal Orthopaedic Hospital.
His mother, an Indian immigrant, tearfully recalled the sacrifices that helped him achieve that.
"We were very poor, we were working hard, I used to cook and sell food to have some money for private tuition," she said.
Khan's body was escorted from Syria on December 22 by the Red Cross to family members waiting in Lebanon.
Arriving back in Britain, the body underwent a CT scan and a post-mortem, before his burial on December 26.
A British inquest to establish the cause of death is due on February 27.