Promptly Prosecute Offenders, Address Underlying Causes (Dakar) - Deadly election-related and communal violence in northern Nigeria following the April 2011 presidential voting left more than 800 people dead, Human Rights Watch said today. The victims were killed in three days of rioting in 12 northern states. Nigeria's state and federal authorities should promptly investigate and prosecute those who orchestrated and carried out these crimes and address the root causes of recurring inter-communal violence. The violence began with widespread protests by supporters of the main opposition candidate, Muhammadu Buhari, a northern Muslim from the Congress for Progressive Change, following the re-election of incumbent Goodluck Jonathan, a Christian from the Niger Delta in the south, who was the candidate for the ruling People's Democratic Party. The protests degenerated into violent riots or sectarian killings in the northern states of Adamawa, Bauchi, Borno, Gombe, Jigawa, Kaduna, Ka