The family placed flowers by a pair of weathered cowboy boots, as people quietly gathered for the memorial of the soft-spoken tribal chairman who mentored teens in the boxing ring and teased his grandkids on tractor rides. Left unsaid, and what troubled Marvin Cota’s family deep down, was that his story ended like so many others on the remote Duck Valley Indian Reservation. Until recently, a now-razed U.S. maintenance building where fuel and herbicides were stored — and where Cota worked — was thought to be the main culprit.