NEW : Jose Reyes Ferriz mayor says authorities believe drug gang attacked rehab center . Slayings add to grim statistics for the Mexican Citizens Council for Public Security , ranked deadliest city in the world . An unprecedented wave of violence has washed over Mexico since Calderon declared war on drug cartels shortly after coming into office in December 2006 . On March , No . 3 security official in Michoacan state , 2 others , shot to death . Mexico has seen wave of violence since president declared war on drug cartels .
NEW : Jose Reyes Ferriz mayor says authorities believe drug gang attacked rehab center . Slayings add to grim statistics for the Mexican Citizens Council for Public Security , ranked deadliest city in the world . On March , No . 3 security official in Michoacan state , 2 others , shot to death . Mexico has seen wave of violence since president declared war on drug cartels .