Mexicans march to mark the 55th anniversary of the bloody massacre of students in 1968 in the Tlatelolco neighborhood of Mexico City. Five decades on, it remains unclear exactly how many people were killed when the army opened fire on a rally of about 8,000 students in the Plaza of Three Cultures. The massacre -- which came just 10 days before Mexico City hosted the 1968 Olympics -- remains one of the darkest episodes in a year of global turbulence. "They say only a few people died, which is not true. Hundreds of people died here," says 70-year-old Concepcion Jimenez, who was present at the 1968 protest. IMAGES AND SOUNDBITES