"This has been giving officials cause for concern that the bomb was perfectly made and we have never seen such a bomb in Delhi. Maybe, it was made by foreign experts," said Gupta.
Gupta further said it is premature to say who planted or made the bomb.
Sources involved in the investigation said that sticky bombs and silencer-fitted weapons are the latest tactics being adopted by insurgents in Baghdad and other places.
Sometimes there are several such attacks a day, usually targeting government or security officials with pinpoint accuracy.
The official added that by sticking a small bomb under a vehicle or using a silencer-fitted weapon, the attackers can operate quickly and without drawing much attention to themselves.