By Mick Krever, CNN

It is “more and more likely” that chemical weapons were used in an attack outside Damascus, a Chemical, biological, and nuclear threat analyst told CNN’s Hala Gorani on Wednesday.

“Initially what I thought is that it could well be a concentrated riot control agent,” Gwyn Winfield said. But “as the footage has sort of gone on, it looks more and more likely that some kind of organophosphate – so that is some kind of nerve agent – has been used.”

Survivors, portrayed in videos posted online, are “showing more sort of typical chemical warfare agent signs and symptoms.”

Winfield was not able to identify what type of agent may have been used, but said that it did not appear to be a “pure weapons-grade” attack.

“It may well be that this was some kind of an Assad homebrew,” he said, “where he has managed to get elements of an organophosphate, mix it with other chemicals, and then delivered it onto these people.”

The only way to know, he said, for sure will be to get hair, and possibly blood samples from alleged victims, and bring them to a laboratory.

“The next forty-eight hour window is going to be crucial,” Winfield explained.

After that, the concentration of “certain key elements” in the bloodstream will start to fall, making detection more difficult.

“The agent itself – it could be a gas, it could be a vapor, it could be an aerosol – will now have dispersed,” he said, though added that some evidence may remain in the soil.

“We’ve yet to work out exactly who delivered these munitions,” Winfield said, “but the one thing that we are sure of, when you look at the amount that’s used, is it has to have been a military. This isn’t a small rogue element; this isn’t a small group. This is a concentrated, well-organized attack by a significant player.”