HERAKLION, June 7 -- He had kept a low profile for nearly two years, renting a room in the eastern Cretan town of Agios Nikolaos while working seasonal shifts at a nearby hotel. His Athens apartment, on Acharnon Street in the Kato Patisia district, told a different story. When Greek counterterrorism officers forced the door on Saturday, they found precision laboratory scales, radiation dosimeters, a magnetic hotplate stirrer, and an array of chemical reagents - the components, investigators say, of a bomb-making operation that had not yet reached its final stage only because the precursor chemicals he had ordered online had not arrived.

The man, a 37-year-old Palestinian national from Gaza who has not been publicly identified by Greek au...