explosive used in their vest. >> we want to understand those vests as our officer rush in. we want to give them intelligence of what they might be up against. >> reporter: they were loaded with tatp. it's a homemade explosive with a sinister nickname. "mother of satan," a name coined by terrorists because it's sensitive to heat, volatile and can potentially cause extreme damage. experts say it's also cheap with ingredients that are easy to come by. >> 90% of the stuff we have here, you don't need a license to buy. i can go in a truck about a half hour away and come home with 90% of this. >> reporter: paris is not the first time tapt has been traced to terrorist attacks. richard reid is arrested with a device hidden in his shoe, tatp.