Investigators in India have no suspects in the aftermath of a deadly triple bombing Wednesday that killed 17 people and injured dozens more.
Officials had initially said 21 people were killed in the co-ordinated blasts, but later downgraded the death toll to 17, with 131 injured.
The bombs detonated between 6:45 and 7:05 p.m. local time on Wednesday, in three busy neighbourhoods packed with commuters heading home from work.
CTV's South Asia Bureau Chief Janis Mackey Frayer said investigators were considering all possibilities in their search for suspects.
"The fact these explosions were simultaneous suggests co-ordination and it's why the home minister today was saying nobody, no individual and no group is off their radar in this investigation," she told CTV's Canada AM on Thursday.
The triple bombing was the worst India has experienced since terror strikes in Mumbai killed 166 people in 2008.
No group has come forward to claim responsibility for Wednesday's attack and officials have declined to speculate about who might be behind the violence.
Indian Home Minister Palaniappan Chidambaram said there was no warning that an attack was imminent.
"Whoever has perpetrated this attack has worked in a very, very clandestine manner," Chidambaram said at a news conference after an emergency security meeting.
He added that police were considering ""every possible hostile group" in their probe.
In the past, India has accused Pakistan of supporting terror groups that carry out attacks in India. However, Pakistan's president and prime minister quickly condemned Wednesday's violence.
"Right now there are very few clues that police and investigators are working with to try and piece together who is behind this," Mackey Frayer said. "They're thinking it could be a group with ties to Pakistan or it could be the Indian Mujahideen."
Officials from India and Pakistan are scheduled to sit down for a new round of peace talks in a few days, and some have suggested the bombings were aimed at derailing the talks.
"We are ruling out no hypothesis," Chidambaram said.
The three bombs, or improvised explosive devices, were situated in open, heavily trafficked areas.
In the Dadar area in central Mumbai the bomb was placed on a bus shelter. In the Opera House business district in southern Mumbai it was hidden under some garbage on the road. And in the Jhaveri Bazaar jewelry market it was hidden under an umbrella, near a motorcycle, officials said.
The bombs were made of ammonium nitrate and incorporated electric detonators, authorities said.
"The IEDs were not crude and showed some amount of sophistication and training," said R.K. Singh, India's home secretary.
Surveillance cameras were in place at all three blast sites, but it was not clear whether any information was gleaned from them.
International terrorism and security expert Alan Bell said the 2008 Mumbai attacks set a new standard for terrorism, and the Wednesday bombings seemed to follow a similar model.
He said terrorists learned from the 2008 violence that several co-ordinated attacks, in different parts of the city, could strike deep fear not only in residents, but in emergency service workers afraid to respond due to the risk of further explosions.
"They know that when one bomb goes off everyone can respond to it but you get three or four bombs going off simultaneously and it stretches out the emergency services and the security services and they're more nervous going into those situations because they know there could be five, six or seven bombs," Bell told Canada AM.
Though the death toll was reported to be 21 on Wednesday, Chidambaram lowered the total to 17 confirmed deaths on Thursday.
He said a severed head was found that could be an 18th casualty but did not explain the discrepancy from the earlier count of 21 dead.
Additionally, 131 were injured, 23 of them seriously.
With files from The Associated Press
