Hair and prints were reportedly found on Reid's shoes
American news reports say hair and palm prints have been found on the shoes, which have been the subject of several tests since Mr Reid's arrest on 22 December.
Mr Reid, a Briton coverted to Islam, allegedly tried to set fire to explosives in his shoes while on an American Airlines flight from Paris bound for Miami. He denies the charges.
He was overpowered by passengers and sedated by an on-board doctor until the flight was diverted to Boston's Logan Airport, where he was arrested.
American news channel CNN says the FBI has concluded that the presence of such samples means Mr Reid was aided in assembling the bomb.
Powerful explosive
Mr Reid is said to have told investigators that he used a recipe from the internet to make a rare explosive known as TATP, or triacetone triperoxide.
He said he bought the ingredients from either a Czech or Slovak man in Amsterdam, one of the many places he travelled through.
He also said that he acted alone.
The TATP would have been used to set alight more powerful explosives called PETN, which experts say would have been powerful enough to blow a hole in the side of the plane and cause it to crash.
According to the French newspaper Le Parisien, the reported discovery of TATP links Mr Reid to two Islamic fundamentalist groups linked to Osama Bin Laden's al-Qaeda network.
Mr Reid was formally charged last week in a Boston court with attempted murder and attempted destruction of an airliner.