The development follows Centre's direction for hand-over of the case to NIA, sources said, adding that NIA, which had already started its probe, would continue it.
FIRs (one for each blast) were registered under relevant sections of Indian Penal Code and other Acts.
"The CD (crime diary) files pertaining to the case, which was so far being probed by the SIT of Andhra Pradesh police, will also be handed over to the NIA," a senior police officer told PTI.
NIA has questioned two suspected IM operatives, namely, Syed Maqbool and Imran Khan. Yesterday court granted it custody of another suspected IM operative, Obaid-ur- Rehman.