Couple of OZ surfers missing in Mexico

Reading about it in Aussie press it seems to indicate they were driving at night and possibly headed off the road to boondock in an area known to be frequented by cartels. They were observed buying amap at an all night convienience store in Los Mochis which indicates they were traveling after dark. I wonder if they stumbled into something they were not supposed to see, or on the other hand they may have cooked something inside the van, overcome with fumes, then a fire. All speculation, but driving at night in remote areas is not particulary advisable.