A man was arrested Monday in the shooting death of a journalist who worked for the newspaper El Heraldo de Chiapas, and authorities were searching for three other people suspected of having ordered the killing.Luis Alberto Sanchez, a homicide prosecutor in the southern state of Chiapas, said in a video statement posted online that the detained man is believed to have acted as a lookout outside the home of reporter Mario Gomez.Sanchez said the man allegedly belonged to a local drug gang and identified the gang’s leader, his right-hand man and the . . .