WITH THE THIRD INFANTRY, Central Iraq, Saturday, March 29 — A Iraqi suicide bomber killed five U.S. soldiers today by luring them to his taxi cab at a checkpoint north of Najaf and then detonating an explosive, an army spokesman in the region said. The attack occurred north of Najaf on a road west of the Euphrates River. The victims were all members of the division's First Brigade, which has been involved in significant fighting around the city since last weekend. Capt. Andrew J. Valles, the civil affairs officer for the First Brigade, said the attack occurred just after noon...