US and Afghan intelligence intercepted phone calls from Inter-Services Intelligence (ISI) officials in Pakistan, hearing them plan the attack with militants in Kabul days before the bombing on July 7, 2008.
At the time, intelligence officials monitoring the phone calls did not know what was being planned, but a high-level ISI operative's involvement in promoting a terrorist attack was clear, says The Wrong Enemy: America in Afghanistan 2001-2004, by journalist Carlotta Gall.
Investigators found the bomber's cellphone in the wreckage of his explosives-laden car. They tracked down his Afghan collaborator in Kabul, a man who provided logistics for the attack.
In the book, released next month, Gall writes that the collaborator was in direct contact with Pakistan by telephone, and the number he called was that of a high-level ISI official in Peshawar. The official had sufficient seniority that he reported directly to ISI headquarters in Islamabad, according to the book.
It is no small coincidence that some of the grenades used in the 2008 Mumbai terror attacks were also traced back to the POF unit in Wah. The grenades were manufactured by POF under licence from an Austrian firm.
American officials also said at the time of the Kabul bombing that members of the Haqqani network, which is based in the North Waziristan tribal region of Pakistan, were involved in the attack. The suicide attack killed 58 people, including defence attaché Brigadier Ravi Datt Mehta, Indian Foreign Service officer V. Venkateswara Rao, two Indo-Tibetan Border Police personnel, and injured over 140.
Due to the alerts from US and Afghan intelligence, security at the Indian Embassy was strengthened before the attack. The suicide bomber struck just as the mission's main gate was opened to let in a car carrying Brigadier Mehta and the IFS officer.
Prime Minister Manmohan Singh had raised Pakistan's role in the attack with his then counterpart Yousuf Raza Gilani on the sidelines of a SAARC summit in Colombo in August 2008. After initially agreeing to look into India's concerns, Pakistan later contended there was "no evidence" of ISI's involvement in the attack.
Gall writes in her book that the bombing of the Indian Embassy was not a "subtle attack needling an old foe" and the plan was to send "a message not just to India but to the 42 countries that were contributing to the NATO-led international force to rebuild Afghanistan".
Her book has already created a furore in Pakistan after an excerpt carried recently in The New York Times stated that the ISI ran a special desk to handle Al Qaeda chief Osama bin Laden, who was killed in a US raid in Abbottabad in May 2011.
The book also claims there was regular correspondence between bin Laden and Pakistani jihadi leaders like Lashkar-e-Taiba founder Hafiz Mohammed Saeed.Pakistan denies these claims.