Abdul Halim, an activist of the Students Islamic Movement of India, who was arrested in connection with the Ahmedabad serial blasts, was remanded to police custody for 14 days by a city court on Monday.
The Ahmedabad Crime Branch also launched a massive operation to track down others involved in the blasts.
"Suspects, those who have been detained by us, are being questioned at present. Abdul Halim, a SIMI activist, who was arrested in connection with the blasts, is also being questioned," 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.
Bhatia said the police have not issued any sketch of suspects so far and added that efforts are on to find out details of the car used in the blast at the Civil Hospital.
The registration number of the car was that of a two-wheeler, he said.
When asked about detention of Sikh youths in connection with the serial blasts, Bhatia said, "We are questioning people from all communities. Several people are being detained and questioned, which include a few from the Sikh community. We are questioning people who may be witnesses or suspects. Investigations are going on and we will not take the name of any group at present."
The police have also sent contents of the live bombs found in the city on Sunday for analysis to the Directorate of Forensic Science, Gandhinagar.
The forensic officials have also conducted detailed studies at the blast sites and have collected material for further probe.
Health Minister Jaynarayan Vyas, who is also the government spokesman, said, "It would not be proper to name any organisations before the security agencies involved in the investigations find out the truth about who were behind the blasts".
The state government has formed a special committee headed by Principal Secretary (Home) Balwant Singh to coordinate with Central security agencies and state agencies probing the blasts.