Kananga - A man believed to be a leader in the Democratic Republic of Congo's Kamwina Nsapu militia has been detained over a beheading in the troubled Kasai region, a judicial source told AFP on Thursday."He was arrested on Tuesday. For now the presumed militia chief is undergoing questioning from military justice," said the source, adding that the man was believed to be a leading figure in the Kamwina Nsapu rebel group.He is suspected of ordering the decapitation of six people who were supervising exams at a school before they were ambushed on May 31.Although regional authorities paid a ransom, the militia chief, Ngalamulume wa Ngalamulume, ordered the decapitation of four school inspectors along with a ministerial advisor and his driver, the source told AFP.Violence in the region has left more than 3 000 people dead since last September, according to a tally by the Catholic Church.UN personnel have uncovered more than 80 common graves and put at 1.4 million the total number of people displaced by the unrest. Two UN experts were killed in March while investigating the unrest. One was beheaded.The violence erupted in August last year after a local tribal chief, Jean-Prince Mpandi, was killed in clashes with security forces after rebelling against the authority of President Joseph Kabila's regime in Kinshasa and its local representatives.The death of Mpandi - known by the tribal title of Kamwina Nsapu - and the failure to give him what was considered a proper funeral sparked an insurrection, which led to a brutal government crackdown.