Julia Laureta, mother of Luis Gerez, a 51-year-old construction worker who vanished on December 27, 2006, wipes her tears next to a picture of him during a demonstration to demand his safe return in Escobar, some 50 km (31 miles) north of Buenos Aires December 29, 2006. Gerez was a witness earlier this year in a congressional investigation probing whether a former police chief accused of rights abuses and recently elected to Congress should be allowed to take his seat. Gerez is also the second 'Dirty War' (Argentina's military dictatorship) witness to go missing.