An FBI special agent told a court today that the Briton accused of trying to ignite explosives in his trainers was carrying a "home-made bomb."
It was also reported Mr Richard Reid from London told the FBI that he purchased the explosive materials from a dealer he found on the internet.
It is claimed Mr Reid says he spent £1,000 sterling on the plastic-explosives component PETN during a visit to Amsterdam.
Mr Reid (28) appeared today at a detention hearing in a Boston court wearing an orange jumpsuit and with his hands shackled.
He has been held without bail since Saturday, when he was arrested after American Airlines attendants saw him try to touch a lit match to his trainers during a Paris-to-Miami flight.
Mr Reid was overpowered by flight attendants and passengers, and the plane was diverted to Boston.
Prosecutors were expected to ask Magistrate Judge Ms Judith Dein to hold Mr Reid without bail until trial.
FBI Special Agent Ms Margaret Cronin, a specialist in crime aboard aircraft, testified that the FBI had determined Reid was carrying "functioning improvised explosives, or, in layman's terms, a home-made bomb."
Muslim convert Mr Reid was charged with intimidation or assault of a flight crew, which carries a maximum 20 year sentence, but the FBI has indicated that additional counts are likely.
US investigators are casting a wide net in a global investigation to determine whether the man had any ties to terrorist groups. Officials in Israel, France, the United States and the Netherlands have been retracing Mr Reid's travels ahead of his apparent botched attack on Saturday.
US government officials said Mr Reid's plan may have been foiled in part because the material he used as a fuse was difficult to light.
Testing showed indications of PETN, a material used to make the explosive Semtex, the same explosive used by Libyan terrorists in 1988 to down Pan Am Flight 103 over Lockerbie, Scotland, the officials said.
They said a nonmetal fuse in the shoes could have picked up enough moisture to make the explosives difficult to light.
Authorities said they haven't drawn any conclusions about whether Mr Reid had accomplices.
Some officials who have been briefed on the investigation said the information being gathered about Mr Reid suggests he may have had help. They specifically cited the construction of the bombs in his shoes.
"I would doubt very seriously he did it by himself," said Representative Mr John Mica, chairman of the House aviation subcommittee.
But assistant federal public defender Tamar Birckhead, one of Mr Reid's court-appointed lawyers, said she was unaware of any evidence linking Mr Reid to terrorists.
"We urge the press and the public to maintain open minds as the criminal justice system proceeds," she said.
US officials are trying to corroborate claims from some low-level al-Qaeda prisoners that Mr Reid trained with them at Osama bin Laden's terrorist camps in Afghanistan. They warned that the prisoners could be wrong, or lying to confuse or gain favour with their interrogators.
Officials have also confirmed that Mr Reid attended the same London mosque as Zacarias Moussaoui, who is charged with conspiracy in the September 11th terrorist attacks.
AP