Jemaah Islamiyah
Jemaah Islamiyah is known to use pressure cooker bombs with RDX and like explosives with taggants. Note that Jemaah Islamiyah had operatives in the Pakistan areas active in religious indoctrination and that were working with Egyptian Islamic Jihad through al-Zawahiri who taught on the use of pressure cooker bombs. As such it is quite possible that Jemaah Islamiyah was involved in the attack possibly through Indian Mujahideen which it also forms part of.