YUSUFIYA, Iraq (Reuters) - Two slain U.S. soldiers who went missing south of Baghdad were ambushed by as many as 30 insurgents who closed in on them in vehicles and opened fire, according to people who said on Wednesday they were witnesses. It was not possible to independently verify their accounts. The U.S. military has yet to explain how the soldiers may have been isolated in what Iraqis call "The Triangle of Death" for its frequent insurgent attacks. But two Iraqis who said they were witnesses gave similar accounts of the moments when Privates First Class Thomas Lowell Tucker, 25,...