The glare of the headlights of three blacked-out SUVs screeching towards us was the first bad sign.

Actually, that’s not true. The first bad sign was hours before that, when our cobalt-blue Mitsubishi pick-up truck sank into the sand on the edge of one of the most dangerous stretches of the US-Mexico border.

As our truck ground to a halt, we spotted a group of people-smugglers 200 metres away, fanning thick plumes of smoke from a fire they had built to disguise migrants crossing into New Mexico.