Dr Ahmad and two other volunteers travelled to the attack sites to collect evidence in a mission that ran the gauntlet of kidnapping, arrest, shelling and air strikes.
"I did this for the simple reason that I wanted to show the world that chemical agents had been used," he said after arriving in Turkey, with samples labelled and bagged. "I did it methodically. I filmed everything. I wanted to be sure that I have the whole chain of custody without interruption [from collecting the samples to seeing them tested] so when the results come, we know that they are accurate."
Dr Ahmad, a medic in rebel-held Aleppo, first took an interest in chemical weapons during an attack on the city in March last year.
"There was chaos in the hospitals. Doctors became contaminated treating the wounded. People were so afraid and didn't know what to do. I studied the process of decontamination and medical treatments on the internet."
Later in the year, he was part of a group of Syrian medics trained by Western chemical weapons experts in how to react in a chemical attack and the procedure for collecting samples in the aftermath.
