The reply that began this thread is hysterical and ignores the facts.
The three men were convicted of
plotting to blow up the aircraft; it is irrelevant whether their plot would have succeeded or not. They were filmed preparing the devices, and suicide videos were found in which they bragged about the attack and talked of body parts littering the streets.
Furthermore, according the the Guardian:
Video footage of tests conducted by government scientists, which were played to the jury, showed the devices producing an explosion powerful enough to blow a hole in an aircraft fuselage.