Mother Agnes argues in an interview with BBC on Tuesday, the horrifying scenes - of men, women and children either dead or dying from inhaling sarin gas - which caused such international outrage were stage-managed.
The videos formed an important part of the evidence used by much of the international community to argue that regime forces carried out the attack.
Mother Agnes said to have carried out an exhaustive study of the videos and in a detailed report says she has found evidence of manipulation.
She noted the body of the same child can be seen in several different videos filmed in separate locations. "Why should they take a corpse to many locations?" she says.
"It is evidence my dear... I am not a commission of inquiry, but for me it is sure. I have evidence that confirms there's been manipulation of the corpses."
In her most startling conclusion she says some of the people seen in the videos are in fact women and children abducted by the militants from minority Alawite areas of the country. President Bashar al-Assad and his family belong to this community.
"Some families of the abducted people contacted us to claim that some of the children presented as victims of chemical attacks are in reality their own children," says Mother Agnes.
"They recognized them and asked us to find out what happened to them."
After completing her report, Mother Agnes distributed it at the United Nations in Geneva.
Mother Agnes's work normally revolves around the Catholic monastery of St James the Mutilated, which lies north of the Syrian capital. Although she is Lebanese, it has been her home for decades.
In recent weeks she has become the focus of media attention because of her attempt to prove to the world that Syrian opposition activists fabricated the videos showing victims of the Damascus chemical attack.
Syrian opposition groups claimed hundreds of people were killed during a fierce government offensive against militant-held areas, and some activists claimed regime troops used "poisonous gas". However, the Syrian government denied its troops used chemical weapons.
NTJ/BA