The Ahmedabad [Images] Crime Branch on Monday questioned Abdul Halim, an activist of the Students Islamic Movement of India, who was arrested in connection with the serial blasts, as it launched a massive operation to track down those involved.

"Suspects, those who have been detained by us, are being questioned at present. Abdul Halim, a SIMI [Images] activist, who was arrested in connection with the blasts, is also being questioned and he is likely to be produced in court for remand," Joint Commissioner of Police (crime branch) Ashish Bhatia, who is heading the probe, said.

Halim was allegedly involved in recruiting people for Jehadi activities, the police said.

Sixteen blasts in the span of 60-70 minutes rocked the city on Saturday, killing 49 people and injuring over 145.

The police also conducted raids in different parts of the city last night and detained many people for questioning, Bhatia said.

The crime branch is also tracking cycles used in the serial blasts held in Ahmedabad on Saturday. As per police sources, most of the cycles used in the blasts were second-hand ones.

The police questioned some of the cycle dealers of the city to find a lead, the sources said.

The police were also talking to a person who claimed that he had seen suspected bombers parking cycles in Raipur, which was one of the blast sites.