Delhi police have a reasonable description of a man who planted one of the bombs in Saturday's triple blasts, a senior official said on Monday.
A passenger spotted the bomb, kept in a black sling bag on a bus, and alerted the conductor and driver of the bus.
The bus driver was injured when he threw the bomb out of bus, saving at least 10 lives.
"We had appealed to the passengers of the bus to come forward and identify the culprit through the newspapers.
"Some of them spoke to us and have given descriptions. We would again like to appeal to the passengers through the media that they should come forward and help us in piecing together the information so that we could go after them," Joint Commissioner (Crime Branch) Karnail Singh told a crowded press conference.
At least sixty persons lost their lives and over 200 persons were injured in what Prime Minister Manmohan Singh described as a dastardly crime.
The joint commissioner showed replicas of the two bags used by the terrorists in separate incidents and appealed to the shopkeepers who may have sold similar bags bearing the name Nike so that they could start looking for the buyers who may have bought the bags in recent days.
While confirming that the Delhi police teams have been sent to Punjab, Uttar Pradesh and Jammu and Kashmir, Karnail Singh refused to share the information gathered in the last 48 hours to nab the group behind the attacks.
"It looks the work of the same group. Forensic reports have not come in as yet. The kind of timer used in the explosions would be known only after that," he said.