Even as the police scramble for more clues, the Intelligence Bureau has sent an advisory asking all police personnel across the country to be on high alert.
Sources said the May 25 blasts now appears to have been a trial run for Wednesday's strike. There are too many similarities between the two incidents, and the same people could be involved, they said.
A Delhi police official said they want to gather details about the bomb's composition before ascertaining the nature of the blast, but at the moment it appears to be a medium-intensity explosion. The bomb composition will provide leads on the outfit which could be behind the attack, say Delhi police officials.
They added that for now the focus is on bringing the situation under control and also taking care of those who have been injured.
Several teams have been pressed into action at the moment including the NIA, National Security Guard, and a team of forensic experts apart from the Delhi police.