A secret al-Qaeda document discovered at Osama bin Laden's hideout in Pakistan sets out a strategy for attacking economically important targets including "pipelines, internet cables and tankers".
The document, written by the al-Qaeda planner Younis al-Mauretani, suggests planting recruits in jobs that later could be useful in attacks, such as oil or gas transportation, and directing supporters to study chemistry and physics.
The US Department of Justice passed the letter to German prosecutors last year for use in a trial in Dusseldorf, according to the German newspaper Die Zeit.
Three FBI agents were in court in Dusseldorf on Wednesday to give evidence about the authenticity of the letter. Three defendants in the case are accused of plotting a bomb attack in Germany under the direction of al-Qaeda.
A Moroccan recruit mentioned in the letter has the same date of birth as one of the defendants in the Dusseldorf case.
The plan, which was sent to bin Laden in March 2010, proposes attacks against large tunnels and bridges, dams and financial centres. It also suggests attacking think tanks, and names the Rand Corporation, a US government-funded research institute in California. The Love Parade, a dance music festival in Germany, is another proposed target.
The letter says that al-Qaeda should continue using aircraft, but that its pilots should fly regularly with airlines before carrying out an attack. The co-pilot could be drugged with sleeping pills before an operation, the letter suggests.
The 17-page document includes a suggestion that al-Qaeda should use submarines to explore the layout of underwater gas pipelines, in order to mine them. This idea is given serious consideration in the document which notes that the pipelines have safety valves every six miles that need to be taken into account when planting mines.
Pakistan's army announced in 2011 that it had captured al-Mauretani in the south-western city of Quetta.
Yassin Musharbash, an investigative reporter with Die Zeit, said there were no explicit references to Britain in the document. Defence lawyers in the Dusseldorf trial say they have "fundamental doubts" about the veracity of the document, according to the newspaper.