KANO - Gunmen have killed the justice commissioner for a Nigerian state at the heart of an insurgency and an ex-prisons chief in another area, government and police sources said Tuesday. It was not immediately clear who was behind the killings, but they occurred after security forces on Monday shot dead two suspected high-ranking members of extremist group Boko Haram. In Borno state, gunmen stormed the justice commissioner’s home late Monday in the town of Bama in the country’s northeast, the region where Boko Haram is based and which has been hard hit by gun and bomb attacks.