India's home secretary says detectives are examining forensic evidence and surveillance video, as they hunt for clues into the deadly bomb blasts that hit Mumbai earlier this week.

R.K. Singh said Friday authorities have identified a scooter which they said contained one of the bombs. A total of three blasts occurred within 20 minutes of each other in India's financial capital Wednesday, killing at least 17 people and wounding 133 others.

Singh said they are questioning people on the basis of the government's criminal databases and previous known links to terror groups.

Detectives also are in the process of viewing the large amount of surveillance video from the sites of the explosions, looking for suspicious people or activity. So far, authorities have not announced any big breakthroughs in the case.

While they refuse to speculate on who might be responsible, officials have said they are pursuing all leads, including the possibility that home-grown terrorist groups or the city's criminal gangs were involved.

Officials also say Indian intelligence had no warning before the bombings. No one has claimed responsibility, but authorities say they believe it was a “coordinated terror attack.”

Forensic examination of debris at the sites already has indicated that ammonium nitrate — a common fertilizer ingredient — was used in the explosives. Officials say the improvised explosive devices used indicate some level of sophistication.

Prime Minister Manmohan Singh arrived in Mumbai Thursday to visit with the victims and speak with authorities.

Wednesday's attack was the worst to hit India's financial hub since Pakistan-based militants laid siege to the city in 2008, killing 166 people.

Peace talks between the two countries were suspended following that attack and have just recently resumed. The Pakistani government condemned the violence immediately after the blasts.