“We have to verify with Bangladesh whether there is anything common between Shafia’s father and the complainant in Dhaka,” Hyderabad police commissioner Balwinder Singh said.

Police admit that Rizwan and his friends could just be illegal immigrants but admit that one strong line of investigation is the possibility that a Bangladesh or Pakistani national may have carried out the attacks. Initial searches in madrasas around Hyderabad revolved around finding illegal immigrants staying without valid papers.

Sources said the police zeroed in on one such illegal Bangladeshi immigrant 20-year-old Rizwan Ghazi living in the Kishanbagh area of Hyderabad’s Old City.

The search of Ghazi’s house is believed to have led the police to his Vellore-based sister Shafia. Soon after the search of Rizwan’s house, the local police reported, but later denied, the discovery of “small metal balls” used in the explosive devices in the blasts. Although, officially, the search for Rizwan is still on, sources said he is in custody.

On Sunday, the Hyderabad police issued sketches of Rizwan and Shafia’s parents Zainal Abedin Ghazi and his wife, their younger brother Irfan Ghazi, 12, and two others Masiluddin, 24, and Hussaini, 18, both illegal immigrants believed to have been staying with Rizwan Ghazi at his Kishanbagh home.

According to the police, Zainal Abedin Ghazi was a regular visitor to Vellore where his daughter studied and his wife had at one point undergone treatment at the Christian Medical College at Vellore.

“Masiluddin was staying in Hyderabad illegally and was involved in a cloth business. He left the city a month after the May 18 blasts. Hussaini left around August 29. We are investigating them,” the assistant commissioner of police of the Charminar area said. “We have seized some material from the Kishanbagh residence,” ACP Reddana said.