The four blasts, which targeted two synagogues and British interests in Turkey's commercial capital, killed 61 people and wounded several hundred others.
"The suicide attacks were carried out by elements trying to organise for al-Qaida in Turkey," city governor Muammer Guler told a news conference in Istanbul held on Friday to announce progress in the investigation.
"We can comfortably say that we have broken up the organisation's Istanbul activities," he said.
The governor said 35 people have been charged so far in connection with the attacks and that a further 10 people were sent on Friday to a state security court which will decide whether they too should be charged.
One of those sent to court on Friday, Harun Ilhan, was also taken to the site of the Neve Shalom synagogue in the city, where one of the blasts occurred, to help recreate what had happened.
Media reports said Ilhan had confessed to being a member of Usama bin Ladin's al Qaida network and said he had lived for a year in Afghanistan after evading military service in Turkey.