Investigators probing the multiple blasts in Bodh gaya temple believe that at least three to four terrorists visited the complex to plant the 13 bombs as each explosive might have weighed four to five kg with cylinder.
Official sources said the investigators were scanning the footage of CCTV installed in the complex to locate those who were carrying the bombs - possibly in bags or cartons - but the quality of pictures were not so much of helpful to identify the persons.
"At least three to four people must have carried the bombs. But so far, their pictures are not visible in the CCTV footage. The task of scanning the footage is continuing," a source said.
Sources said since the bombs were exploded in the early morning when there were few pilgrims, the perpetrators might have wanted to convey the message that they can carry out a bigger attack whenever they want and elaborately.
Since Bodhgaya is frequented by around 3,000 foreign visitors and a few hundred Indians every day, it was extremely difficult for the security agencies to monitor movement of outsiders in the town.
The security plan being drawn out by the authorities after the July 2 meeting with monastery is yet to be fully implemented and private security personnel continue to guard the historic site.
Use of cylinder technology in triggering blasts seems to be a new practice in India, sources said, adding each of the bombs used on Sunday may have weighed 4-5 kg with cylinder.
They said the National Investigation Agency has not yet taken over the case but helping Bihar Police in its probe.
The Home Ministry has not received any formal request from the Bihar government on CISF personnel providing security.
"When we receive the request, the Home Ministry will certainly consider it," the source said, adding no religious place is so far guarded by CISF but CRPF mans few religious sites.