On a hot pursuit of the two men in black who are suspected to be behind the blast in Delhi on Saturday and with none claiming responsibility for it, the whodunit question is confronting the Delhi police.
Investigations are on to check whether Saturday's blast has any link with other such attacks in other parts of the country and to find out if it was in continuation of five mysterious explosions that had taken place in south Delhi early this year. Delhi Police had earlier claimed that those explosions were not bomb blasts.
An e-mail purportedly sent by Indian Mujahideen had claimed responsibility for the September 13 blasts in the national capital which claimed 24 lives.
Among the five mysterious explosions that took place in Mehrauli, one was near Indian Institute of Technology on January 16 in which one person was injured. A fortnight later, two similar blasts were reported from Malaviya Nagar locality.
Officials said the ingredient of today's bomb was ammonium nitrate in a small quantity along with sulphur and potassium. The bomb was loosely packed and contained one-and- a-half inch nails while sulphur was used to create dark smoke.
Ammonium Nitrate was used in the five serial blasts that shook the national capital on September 13.