WATERTOWN, Mass.—Authorities Friday arrested a 19-year-old college student suspected in the deadly Boston Marathon bombings, following a manhunt that for a full day had paralyzed a metropolis.

Police and Federal Bureau of Investigation agents converged on a house here around 7 p.m., officials said. Before taking him into custody nearly two hours later, authorities exchanged gunfire with Dzhokhar Tsarnaev, who was found hiding in a boat, covered in blood, by a resident checking on his backyard.

...