A series of Twitter gloats today raised questions about the possible involvement of Somali terror group Al-Shabaab in the Boston Marathon bombing. No person or group has yet directly taken responsibility for the attack that killed three and wounded 176, 17 of those critically. The FBI issued a be-on-the-lookout for a dark-skinned or black man in dark clothes, perhaps with a foreign accent, who tried to enter a restricted area moments before the first blast. Authorities were also questioning a Saudi national here on a student visa and searched an apartment in Revere, Mass., last night. Terror groups have shown...