India's home secretary says detectives are combing through forensic evidence and surveillance video, as they continue to investigate the deadly bomb blasts that rocked Mumbai Wednesday.

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

Singh said in his update of the investigation that detectives are combing through 11 CDs of surveillance video from the sites of the explosions, looking for suspicious people or activity.

Forensic examination of debris has already indicated that ammonium nitrate, a fertilizer ingredient, was used in the making of the explosives.

Officials say police are investigating every possible “hostile” group, and that Indian intelligence had no warning before the bombings. No one has claimed responsibility, but authorities say they believe it was a “coordinated terror attack.”

Senior Indian officials have defended the government's security measures in Mumbai and have promised answers, as they face popular anger and grief following the explosions.

Prime Minister Manmohan Singh arrived in Mumbai Thursday, a day after the blasts exploded.

Wednesday's attack is the worst to hit Mumbai since Pakistan-based militants laid siege to the city in 2008, killing 166 people.

Shortly after the explosions, the Pakistani government condemned the violence.

Wednesday's attack also happened just two days after the fifth anniversary of a series of train bombings in Mumbai that killed more than 180 people. Indian authorities blamed that attack on Pakistani militants.