PHOTO CAPTION - SNIPPET: "Officials believe that more members of the so-called Düsseldorf cell may still be at large." SNIPPET: "Halil S. is a man who knows his way around computers. When he went online..." SNIPPET: "German security officials allege that the 27-year-old is the fourth member of the so-called "Düsselfdorf Cell." The group is believed to be the al-Qaida cell currently active in Germany and tasked with carrying out a major attack in Europe. Three other members of the cell, Moroccan Abdeladim el-K. and two accomplices, were arrested in late April and are being held in custody. Authorities believe...