Dr. Ron Medzon, an emergency room physician at Boston Medical Center, recalls treating victims injured in the bombing.
The president of Brazil held an emergency cabinet meeting today to deal with a wave of protests across the country in the last week.
Yesterday more than a million people took part in demonstrations in nearly 100 cities.
The protests started over an increase in transit fares but are now aimed at corruption.
Meanwhile, protests also continue in Turkey.
The BBC’s Katya Adler reports from Istanbul.