Mumbai Serial blast
A policeman walks past a television journalist reporting from the site of an explosion near the Dadar area of Mumbai Reuters

Indian police believe they have seen three men connected to the Tuesday terrorist bombing in Mumbai. Using surveillance camera footage, authorities found three out of place men walking around the area of one of the blasts an hour before the explosion.

Three separate bombs exploded simultaneously in Mumbai Tuesday afternoon, killing 18 people and injuring 130. The blasts occurred in highly populated areas of the city, including the Opera House and the Zaveri Bazaar. Police believe that at least two of the bombs were detonated via cell phone.

After poring over the surveillance tapes of the three suspected men, authorities have some doubts.

Diamond traders...or in any trading in much of it is done on the phone, Maharashtra Chief Minister Prithviraj Chavan told Indian news outlet NDTV Thursday, suggesting that the men are simply doing business.

Monsoon rains have made close circuit video at Zaveri Bazaar, one of the other bomb sites, almost useless. Police have so far not been able to see more than wet umbrellas.

Police are also examining a corpse that was found with electronic circuits on the body.

It is not logical to have electronic timer [on] a suicide bomber. But we are looking at it very carefully. Maybe the body was too close to the impact of the explosion. I would not like to speculate too much on this. Home Minister is looking closely at all this, Chavan told NDTV.

No route, no theory should be ruled out. I have told the police to look even at remotest possibility, he said.

Although no group has claimed responsibility for the bombings, Indian police questioned members of indigenous Islamic militant group Indian Mujahideen.

The Mujahiden has been responsible for a number of attacks in India in recent years, including the 2010 bombing in Varanasi, India, during which a two year-old girl was killed. In the past, the group has used improvised explosive devices similar to those used in Mumbai. Police also discovered a motorized scooter thought to have been used in the attack.

According to Indian Home Secretary R.K. Singh, the bombers planted an explosive inside a motorized scooter and parked it in a heavily populated location. Police have recovered the vehicle and are examining it for clues.