Update: A high-ranking law enforcement official told CBS News that the suspect apparently used a syringe to inject a chemical into the powder, which was located near his groin. It is a technique not seen in previous attempted attacks and it's possible that this incident was a test of whether the materials could pass screening and how effective they might be at causing damage, the source said.
According to Encyclopedia Brittanica, PETN is a highly explosive, colorless organic compound, and is related to nitroglycerin. Introduced as an explosive after World War I, PETN is "valued for its shattering force and efficiency ... and is the least stable of the common military explosives but retains its properties in storage for longer periods than nitroglycerin or cellulose nitrate (nitrocellulose) does."