Messages and floral tributes are seen in Albert Square in Manchester, northwest England on May 23, 2017, in solidarity with those killed and injured in the May 22 terror attack at the Ariana Grande concert at the Manchester Arena. Twenty two people were killed and dozens injured in Britain's deadliest terror attack in over a decade, which officials now say could have been prevented. Ben Stansall/AFP via Getty Images hide caption
Hamidullah Hussaini, 29, taught math to two of the young women killed in a suicide bombing at the Kaaj learning center: Marzia and Hajar. He says they were the best students in his class, and their love of learning inspired him. Pierre Kattar/NPR hide caption
People and security forces gather at the site of deadly bomb attacks Thursday in a Baghdad market. The rare suicide bombings killed and wounded dozens of civilians. Hadi Mizban/AP hide caption
Patients are treated at a hospital after a suicide attack in Kabul, Afghanistan, on Saturday. Dozens were injured. Mariam Zuhaib/AP hide caption