Sky News UK has obtained chilling new evidence of mobile execution buses being used by the Chinese government.It comes less than two years before China hosts the next Olympics - an event it was given after promising to improve its human rights record.Chinas penal system is surrounded by a wall of secrecy, but an investigation by Skys China correspondent Dominic Waghorn found between 3,500 and 10,000 people are put to death each year.The volume of executions has meant China has invented new ways of killing, mobilising and mechanising its execution system. A brochure acquired by Sky News reveals details of Chinas new execution buses now operating across the country.Fitted with lethal injection equipment they can deliver on-the-spot executions. Sky News spoke to a number of people affected by the executions including the family of Nie Shubin who was only 20 when he was wrongly accused of rape and murder.His mother and sister told how he was held in jail for three years, without being allowed to see his family. Nie Shuie said They never let me see him after his arrest. That continued till the end. I never saw him again before he was executed. And nobody told us that he had been executed.Nie was accused of attacking a woman in a field near his home, but only after his execution did another man confess to the attack.In an exclusive report earlier this year, Sky News gathered evidence linking Chinas execution system and its booming organ transplant industry. Amnesty International says the demand for transplant organs may be driving the high number of executions in China.Even by official figures more people are executed every year in China than the rest of the world put together.