BOSTON, Dec 14 (Reuters) - U.S. prosecutors said on Wednesday a Chinese citizen attending the Berklee College of Music in Boston stalked and harassed an activist who posted fliers supporting democracy in China and reported the person's activities to Chinese law enforcement.Federal prosecutors in Boston said that Xiaolei Wu, 25, did so after threatening through the online messaging service WeChat to chop off the activist's hands and demanding the person stop posting "reactionary posters" near campus.Prosecutors said Wu, through a Berklee-focused WeChat group whose 300-plus members included the activist, demanded that any fliers be torn down and said he was reporting the activist to the public security agency in China.U.S. authorities said they believed Wu was referring to either the Ministry of Public Security or the Ministry of State Security in China, "both of which investigate political dissidents, including those who voice support for democracy."In an Oct. 24 email, he told the activist to expect to be arrested upon returning to China and that he believed the individual's family members would receive a "political review" from the Chinese government, the complaint said."