The unsolved murders this April of two undocumented immigrants near Eloy, Ariz., coupled with four remarkably similar 2007 killings in the same area, have again raised the specter of a possible campaign by U.S. vigilantes to murder Latino border crossers. One recently retired police detective warns of 鈥渁 lot of angry, militant white men on the border sitting like hunters waiting for these people to come across.鈥