Two people could have been involved in executing the blast on the Israeli embassy car, one to plant the bomb and the other to trigger it, sources involved in the investigation said Tuesday while admitting that they still have no clue about the explosives used.

A forensic sciences report expected by Wednesday would help investigators know the exact nature of the explosives used in the sophisticated magnetic bomb, the first of its kind used in India, sources said a day after the blast in the heart of the Indian capital.

But it was almost certain that a remote device, like a cell phone, could have been used to trigger the blast after a motorcylist attached the device to the car, injuring four people, including an Israeli woman who is the wife of the defence attache in the embassy. 

This meant that two people were needed to execute the attack, one who planted the bomb and made a quick getaway and the other who triggered it.

There is only a remote possibility that a timer device was used as it was a sticky bomb, sources said.

Delhi Police's Special Cell, which is spearheading the investigation, is also examining the CCTV footage to get some clues about the biker and his bike.

"We are searching for the biker and are going through the CCTV footage to get more clues," said Dharmendra Kumar, Special Commissioner (Law and Order), Delhi Police.

Police have also launched search operations in some Delhi hotels, particularly in Paharganj area near the New Delhi Railway Station.

Sources said that investigators were also working on a theory that home grown terrorists sympathetic to the Palestinian cause could be involved in the attack.

The National Investigating Agency (NIA), India's premier anti-terror probe agency, is likely to join the probe into the Monday bombing.

An NIA team Tuesday morning took a look at the blast site and the car that was badly damaged in the attack. 

NIA director S.C. Sinha was also at the Aurangzeb Road crossing where the blast took place Monday afternoon after a lone biker planted an explosive to the rear door of the Innova car from the Israeli embassy and sped away.

Two passengers from a nearby red Indica were also affected by the blast.

Sinha declined to divulge any details of the probe so far. All he said was the NIA was ready to join the probe if Delhi Police seek their assistance.

"Delhi Police are investigating the case and we will assist them if we are asked for assistance."