Investigators said a knowledge of electronics was required to construct the bomb.
Somehow, the IRA had managed to remove the explosives from the hayshed without the army monitors hearing anything, and had used them to construct the bomb that killed the three police officers at Kinnego.
In a signed statement, Mr. Nichols acknowledged helping Timothy J. McVeigh construct the bomb that killed 168 people and destroyed the Alfred P. Murrah Federal Building, but said he had no prior knowledge of the target or of any other co-conspirators.
The executions caused a public outcry in Britain and internationally as the men had admitted to constructing the bomb, which was intended to be used to destroy a power station, but claimed not to be involved in planting it.
Although Mr. Reid told investigators that he had constructed the bombs himself from materials he bought in Europe, prosecutors said they found evidence that he had help.
Among the natural scientists (most of whom were instrumental in constructing the atom bomb) were Albert Einstein, Enrico Fermi, Edward Teller, Leo Szilard, and Hans Bethe.
However, after MI5 was stung by criticism over its handling of her case, it played down her significance, saying her "value as an atom spy to the scientists who constructed the Soviet bomb must have been, at most marginal".
The 28-year-old son of a retired soldier, Asiri is seen by US intelligence as the primary bombmaking expert for al-Qaida in the Arabian Peninsula, having constructed the "underpants bomb" used in the failed suicide attack by a Nigerian on an airliner over Detroit on Christmas Day.
Mr. Asiri, the filings said, constructed the underwear bomb, using about 200 grams of the explosive PETN, and instructed Mr. Abdulmutallab how to use a syringe to inject a chemical that would initiate a fire, which was in turn supposed to detonate the explosive.
Ibrahim Hassan al-Asiri, a Saudi who is regarded as a key member of al-Qaida's operation in Yemen, is the prime suspect for constructing the two bombs.
The international hunt for those behind the failed attempt to fly bombs on US cargo planes has focused on a Saudi-born extremist linked to al-Qaida in Yemen who is also accused of constructing the Christmas Day bomb.
