NIGERIAN criminals have killed two more student captives abducted from a northern university last week, said a state official yesterday, bringing the total number of executed hostages to five. On Tuesday, armed men stormed Greenfield University in Kaduna state, killing one person and abducting an unknown number of students, the latest in a series of kidnappings at educational institutes that are mostly carried out for ransoms. "Security agencies have just reported to the Kaduna State Government the recovery of two more dead bodies of Greenfield University students, killed by armed bandits today," said Samuel Aruwan, Kaduna's commissioner for its state…