They said no RDX or detonator was used to carry out the explosion.
The explosion had taken place on Sunday, some 50m away from Gate No 3 of Jama Masjid and near a police station just hours after two Taiwanese nationals were shot and injured outside the mosque.
A top official said the probe into the explosion was handed over to the premier special cell of the Delhi police on Monday morning.
A case under the Explosives Act has been registered in the incident.
About the firing incident, he said a case under IPC Section 307 and the Arms Act has been registered and investigations are on.
Investigators have questioned about 30 people following Sunday's incidents.