A police helicopter flies above a security perimeter set at the Place Princesse Elisabeth, in Brussels, on March 23 2016, during searches as part of the inquiry into the terrorist attacks on Brussels airport and at a metro station.
About 20 people were killed on the metro and 14 at the airport in the rush-hour assaults, which came just days after the arrest in Brussels of the main fugitive suspect in November's gun and bomb rampage in Paris. / AFP / BELGA / James Arthur Gekiere / Belgium OUT (Photo credit should read JAMES ARTHUR GEKIERE/AFP/Getty Images)
Chaostrophic
