Dolkun Isa was stopped at the Italian Senate, where he was to speak on Uyghur issues.
Retired soldiers are among the members of 55 families displaced from land claimed by a local businessman.
Sittwe district police are still questioning others in the assault that left one Muslim dead and six others injured.
Before the handover, some predicted that the formerly freewheeling city of Hong Kong had the potential to push mainland China in a more democratic direction. What happened?