Editor's note: This story is based on a 46-page internal al Qaeda document, details of which were obtained by CNN. A senior U.S. counterterrorism official told CNN that U.S. authorities believe it was authored by British al Qaeda operative Rashid Rauf. It was discovered by German cryptologists, along with more than 100 other documents, embedded inside a pornographic movie on a memory disk belonging to a suspected al Qaeda operative arrested in Berlin last year. The German newspaper Die Zeit was the first to report on the documents.
(CNN) -- An internal al Qaeda document reveals new details in the 2006 plot to bring down planes using liquid explosives, including the level of al Qaeda's technical expertise.
U.S. authorities believe the document was written by Rashid Rauf, a British al Qaeda operative at the heart of the group's campaign to strike the UK. It sheds significant new light on the plot to blow up trans-Atlantic airliners departing from Heathrow airport in 2006.
Rauf's notes were part of a treasure trove of al Qaeda documents discovered by German authorities that CNN recently obtained access to.
The conspiracy was broken up on August 9, 2006, two weeks before the plot was set to be launched.
In the wake of the arrests, the UK held several trials and eventually convicted 10 men, including ringleader Abdulla Ahmed Ali and bomb chemist Assad Sarwar, for their roles in the plot. But because of UK regulations on the use of intelligence in court, their links to al Qaeda were not explicitly mentioned in any of the trials.
By the time of the arrests, U.S. and British intelligence agencies, with assistance from Pakistan, had established that Rauf was the point man in the plot, had met some of the plotters in Pakistan, and had been communicating extensively with the cell members in the UK as they prepared for the attack.
But many big questions remained unanswered: When and how had al Qaeda recruited and trained the UK cell in Pakistan? What led them to the plan to attack trans-Atlantic airliners?
Rauf's analysis fills in several important gaps.
Ali had arrived in Pakistan toward the end of 2004. It was his second trip in two years -- and on both he volunteered at a relief agency helping refugees from the fighting in Afghanistan. At trial, he testified that he had become radicalized by the U.S. invasion of Iraq the previous year, and was further angered by the U.S. presence in Afghanistan. When he met Rauf, Ali told him he never wanted to return home, Rauf revealed in the document. Instead, he wanted training to fight jihad in Afghanistan.
Ali was one of several British militants making the same request.
In the winter of 2004, Rauf arranged for terrorist training for the ringleaders of the July 7 and July 21 plots in the tribal areas of Pakistan under the supervision of "Haji," who U.S. intelligence believe was Abu Ubaidah al Masri, a senior member of al Qaeda's external relations unit.
At around this time, Rauf also connected Ali with Haji, who arranged for him to receive basic weapons training. From then on "a big change came over his temperament when he first came and when he left," Rauf wrote.
"He was a very clever, patient brother and a natural leader," Rauf wrote.
Ali returned to the UK in January 2005 but went back to Pakistan in June. Later that year he was joined in Pakistan by Assad Sarwar, the future bomb chemist. Rauf wrote that several other members of the circle also traveled to Pakistan during this period and some expressed their wish to become martyrs.
"We would now send back brothers quickly and not keep them for a long time," Rauf wrote. "This was largely due to the fact that (after July 7) we knew there would be intelligence monitoring of people travelling from the UK to Pakistan."
Toward the end of 2005, Rauf wrote, Ali was sent back to the UK with the task of putting together a plot to hit a wide range of targets.
The rosewater solution
Al Qaeda had yet to come up with the plan to target trans-Atlantic airliners. Rauf wrote that al Qaeda believed the London bombings would make it difficult for Ali to acquire hydrogen peroxide, so he had been taught how to make explosive devices with gas. Eventually, Rauf and others decided the best plan was to smuggle hydrogen peroxide, a liquid, from Pakistan to the UK in rosewater bottles which would be packed to look unopened.
"We then analyzed the various machines that were used for checking baggage and persons at airports. We found it was very difficult to detect liquids explosives," Rauf wrote.
"After analysis that it would be possible to take concentrated hydrogen peroxide on board, the thought came to our mind: would it be possible to detonate the hydrogen aboard an airplane?" wrote Rauf.
That was the moment when the liquid bomb plot was conceived. And ever since it was uncovered, the world's airline passengers have been restricted in the liquids they can carry on board.
"The way they progressed from London bomb plots to airline was very unexpected and brilliant," a senior U.S. counterterrorism official told CNN.
Over the next months, Haji brainstormed about how such devices could be constructed and smuggled onto a plane undetected. "The discovery that hydrogen peroxide could be colored without losing its explosive properties was a major breakthrough," Rauf wrote.
They also decided that they would convert AA batteries into detonators, Rauf wrote. "We also practiced how to open a drinks bottles, empty it, and replace it with Hydrogen Peroxide, to make it seem unopened."
Rauf wrote that al Qaeda believed half a kilo of liquid explosive would without a doubt destroy an airplane, having noted a similar amount of plastic explosive Semtex had destroyed Pan Am Flight103 over Lockerbie, Scotland, in 1988.
Travel records show in May 2006 Ali returned to Pakistan for a third time. Rauf wrote he had been recalled so al Qaeda could train him on how to make the new device.
Sarwar also travelled back to Pakistan shortly afterward. His role would be to support Ali in putting together a plot, and continue al Qaeda's work in the UK after the operation, according to Rauf.
On this trip, Rauf wrote, Ali was questioned at Heathrow on departure and tracked by Pakistan's military intelligence -- the ISI -- when he arrived. The ISI requested local police in the Islamabad area to stop Ali and search his baggage, but they were friends of his family and tipped him off about the ISI's interest.
"We trained (him) quickly, and wanted him to leave ASAP. He was also told to do anti-surveillance measures when he got back and only start work when he was comfortable that everything was clear," wrote Rauf.
Rauf wrote that al Qaeda conducted a successful test run with the bomb components minus the explosives on a flight.
"The purpose of the exercise was to test that none of the components would be checked manually," Rauf wrote.
Rauf wrote that Ali was told to target flights heading for the United States. A few days before his arrest, Ali was monitored looking up flights from Heathrow to North America which would all be in the air at the same time.
Rauf wrote that Ali recruited nine suicide bombers in total for the plot, including several who never travelled to Pakistan, suggesting that number of flights would be hit. He wrote the plan was to bomb the flights at the same time, when they were all in the air.
According to Rauf, Ali was told to record martyrdom tapes for the suicide bombers set to take part in the operation. It emerged at trial that by the time of the arrests, six of the plotters had recorded videos, which they taped in an east London apartment Ali was using as the bomb factory.
Two of those ready to carry out martyrdom operations were not arrested by police, because Rauf's contacts had not yet reached out to them at the time of the arrest, according to Rauf's report.
As the plotters prepared their attack, Rauf was in extensive contact with three of them through e-mails, text messages and phone calls. Rauf wrote that he also used Yahoo Messenger. Rauf set up a system of cell phone communications in which the UK group would regularly change the SIM cards in their phones and provide details of new numbers through coded messages.
Rauf said he had four phones with him at all times in Pakistan -- three to communicate with the plotters in the UK and one to communicate with his colleagues in Pakistan. His report showed he was paranoid that Western intelligence agencies might be able to track his voice and he requested that Sarwar purchase him a "voice changer."
The mastermind detained
As Ali made preparations for the attack he became increasingly concerned he was being followed by British security agencies, Rauf revealed. "I told him not to panic," Rauf wrote.
But soon Rauf himself was the target of an international security operation. He was arrested by Pakistani security services on a bus on August 9, 2006. Rauf recalled that his bus was pulled over by elite Pakistani police wielding Kalashnikovs. He realized he'd mistakenly left his phone turned on, which he believed was how the United States had been able to track him. As he struggled to turn it off, he was taken into police custody, a hood was placed over his head, and he was transferred to an army camp. His arrest prompted UK authorities to quickly round up Ali's UK cell.
Rauf wrote that Pakistani authorities were initially "very happy at pleasing their U.S. masters," but when they found out that Rauf had trained in Kashmir, they feared the U.S. would blame them and blocked the British and Americans from accessing him for questioning.
In December 2007, Rauf escaped from Pakistani custody after a judicial hearing and reconnected with al Qaeda in the tribal areas of Pakistan. Shortly after he escaped, he was able to follow news reports of the prosecution case against the cell members in the UK. "They understood the basic idea of the plot but were unaware of some of the minor details," he wrote.
In the fall of 2008, Rauf set three new al Qaeda plots in motion to attack the West -- an April 2009 plot against Manchester, England, a July 2010 plot against Scandinavia, and a September 2009 plot to hit New York. In a face-to-face meeting in North Waziristan in September 2008 with New York plotters Najibullah Zazi, Zarein Ahmedzay and their alleged conspirator Adis Medunjanin, currently on trial in New York, Rauf requested they return to the United States to launch an attack, according to Zazi's testimony.
But Rauf was killed in a drone strike in the tribal territories of Pakistan in November 2008 during the early stages of planning for the trio of plots against the West.
According to a senior U.S. counterterrorism official, his death was a deep blow to al Qaeda's ability to plot terrorist attacks against the West, as the terror network had no other operative able to coordinate plots overseas with his level of operational tradecraft.
Al Qaeda's initiation of plots against the West fell away during the period of his incarceration, and then again after his death, the official said.