Since coming to power in 2012, Chinese President Xi Jinping has launched an unprecedented crusade against press freedom. Facing censorship, threats from police and sometimes jail, the last few independent reporters - those who don't work for state media serving Communist Party propaganda - are no longer able to sell their articles. Recently, at least four citizen journalists, who were investigating the real death toll from the Covid-19 pandemic in Wuhan, have disappeared. More than six months after their arrests, there is still no trace of them. Our correspondents report.