Over the course of several months, the FBI listened to Zazi's phone conversations. In August 2009, the FBI overheard him speaking about mixing chemical substances. It learned that in July and August 2009 he and his three associates were buying large quantities of hydrogen peroxide and acetone products from beauty supply stores around Denver, Colorado. Workers at the Beauty Supply Warehouse in Aurora, Colorado would later tell CNN that Zazi was "a regular" at the store and had made several recent purchases shortly before his arrest, telling them that he had "a lot of girlfriends." Hydrogen peroxide and acetone are components of triacetone triperoxide (TATP; also known as acetone peroxide)-based bombs. TATP was also used in the 2005 London subway bombings, and by Richard Reid, the "shoe bomber". According to the United States Department of Justice, jpeg images of nine pages of handwritten formulations and instructions for making and handling TATP and other explosives were found in one of Zazi's email accounts; they mention that acetone is found in nail polish remover, and that hydrogen peroxide can be found in "Hair Salon - 20-30%."