The day after a San Bernardino, Calif., couple killed 14 people in a rampage, federal investigators thought they had a crucial bit of evidence.
The childhood friend and neighbor of one of the shooters was believed to be accompanying his Russian wife to a U.S. Citizenship and Immigration Services meeting that afternoon. Officials raced to the scene to bring the two in for questioning and to safeguard against the possibility of a second attack.
But when five agents from the Department of Homeland Security (DHS), dressed in tactical gear, arrived shortly after noon, they were blocked from moving beyond the lobby of the building.