Suspects include financial enemies in Middle Eastern states, Islamic terrorists, hostile members of the Chinese military, or government and organized crime groups in Russia, Venezuela or Iran. Chinese military officials publicly have suggested using economic warfare against the U.S.

In an interview with The Times, Mr. Freeman said his report provided enough theoretical evidence for an economic warfare attack that further forensic study was warranted…

“This is the equivalent of box cutters on an airplane,” Mr. Freeman said.

Paul Bracken, a Yale University professor who has studied economic warfare, said he saw “no convincing evidence that ‘outside forces’ colluded to bring about the 2008 crisis.”