Abu Faraj Farj al-Libbi was taken into custody earlier this week, and the BBC reports that Pakistani authorities claim the interrogation is proceeding apace.
An excerpt:
Speaking in the Malaysian capital, Kuala Lumpur, Prime Minister Aziz told reporters that Libbi's capture was a "good development" in the US-led war on terror.
Libbi is wanted in connection with a string of bomb attacks in Pakistan, including two failed attempts to kill President Musharraf in December 2003, and one attempt on Mr Aziz's life last year.
Omar Saeed Sheikh, February 2002Abu Zubaydah, Faisalabad, March 2002Ramzi Binalshibh, Karachi, September 2002Khalid Sheikh Mohammed, above, Rawalpindi, March 2003Naeem Noor Khan, Lahore, July 2004Khalfan Ghailani, July 2004, GujratAmjad Hussain Farooqi (shot dead in September 2004)Abu Faraj al-Libbi, May 2005"We have no idea about Bin Laden, but certainly al-Libbi is a senior member of al-Qaeda, and we were on the look-out for him for a while.
"I know the interrogations are going on and they are proceeding well," Mr Aziz said.
US intelligence officials describe Abu Faraj al-Libbi as the successor to Khalid Sheikh Mohammed - the alleged mastermind of 9/11 who is believed to have been number three in the al-Qaeda hierarchy.
BBC security correspondent Gordon Corera says Libbi's arrest is the most significant since the capture of Khalid Sheikh Mohammed in 2003.
But our correspondent says reports of him being the network's number three are hard to confirm.
However, there have been reports that he was involved in sending messages to al-Qaeda cells overseas with instructions to carry out attacks last year.
Al-Libbi is also a suspect in the death of murdered U.S. journalist Daniel Pearl.