Three Maruti cars with ammonium nitrate, plasticisers and programmable time devices (PTDs) planted in them were used in the bomb blasts in Guwahati, police said on Saturday.
Three persons, including Nazir Ahmed, from whose mobile the SMS claiming responsibility for the blast by Islamic Security Force (Indian Mujahideen) was sent, have so far been arrested, Inspector General of Police (Law and Order) Bhaskarjyoti Mahanta told reporters in Guwahati.
The bombs were planted in three Maruti 800 cars at Fancy Bazaar, Pan Bazaar and Ganeshguri in Guwahati, while a motorbike was used to carry out the blast in Bongaigaon, he said.
The car used in the Panbazaar blast was badly damaged and the last two digits of the chassis number were missing. Investigations were being carried out with the help of Maruti Udyog Limited, Mahanta said.
The car used in the Ganeshguri blast has been traced to Itanagar and the Arunachal Pradesh DIG (SB) has been approached to help in the investigations, he said.
Two PTD switches were found from Ganeshguri.
The owner of the car with number AS-01-0327 used in Fancy Bazaar blast, Tikendra Saikia from Nagaon, has been arrested, he said.
Police in Itanagr said that the car used in the Ganeshguri blast was sold by a distributor at Naharlagoon in the Arunachal capital to a bank official in New Delhi in 1996.
The white car was paid for by cheque by the bank official, they said.
A pulsar motrobike used in the Bongaigaon blast has been traced to Kahilipara area of Guwahati and a person named Biswa Borgohain has been arrested, the IGP said.
Mahanta said Nazir Ahmed was arrested from Moirabari in Nagaon district. The SMS could be a "diversionary tactic or it could be a lead. We are not ignoring it and keeping all our options open.
"There is not much information on the outfit besides that it was formed in 2000-01 by a section of Muslims to counter bodo militant outfits, BLT and NDFB," he said.
Mahanta said that the CID was also preparing sketches of two persons who were seen moving around suspiciously near the chief judicial magistrate's office.
He appealed to the people to come forward with information that could help the investigation.