A  Mexican police officer patrols the area where the bodies of Óscar Alberto Martínez Ramírez and his daughter Valeria were found on a bank of the Rio Grande in Matamoros,  Mexico. Photograph: Abraham Pineda-Jácome/EPA

The father and daughter lie face down in the muddy water along the banks of the Rio Grande, her tiny head tucked inside his T-shirt, an arm draped ove(...)