At 5 o'clock on the morning of November 13, more than 200 Haitian police officers raided the Grand Ravine area of Port-au-Prince. There was a series of loud explosions, followed by gunfire. For the next six hours, the commotion didn't stop. The neighborhood was under siege.

What had started as an anti-gang operation in a poor and largely forgotten neighborhood — in a poor and largely forgotten country — ended in the summary execution of innocent civilians on a school campus.

The police officers were working with the United Nations Mission for Justice Support in Haiti. It was launched in October, a reboot of a previous mission that had begun in 2004, when thousands of U.N. troops were sent to Haiti following a coup d'etat, tasked in part with restoring stability and reinforcing national police capacities.