I keep coming back round to they were ambushed. Who could pull off an ambush? I've not led an extremely sheltered life over the years, so, unless these guys were super naive, not just anyone is walking up to that trailer and getting in. They'd have to be invited in, or they bulldozed their way in. To me, it looks like the former. If it was the former, they had to know their assailants. People w/grow ops, or just selling, do not invite strangers into their homes. Period. (Again unless they are naive.) LE keeps running through my mind b/c they could pull it off w/o problem. They could have thought it was someone they were meeting w/about their agreement, and the LE would have arrived in an unmarked car, and in street clothes. After they go to CR1s then it is feasible they could go to the other homes, under pretense of "there's been an accident", to get inside those homes easily. Just another angle.
Perhaps no one 'let' them because they were already inside both trailers as guests. All the perp had to do was leave.