NEW : Ciudad Juarez mayor says authorities believe drug lords attacked rehab center . This add to grim statistics for Juarez , ranked deadliest city in the world . On same day , No . 2 security official in Michoacan state , 3 years , shot to death . Mexico has experienced wave of violence since president declared war on drug cartels .
NEW : Ciudad Juarez mayor says authorities believe drug gang attacked rehab center . Slayings add to grim statistics for Juarez , ranked deadliest city in the world . On same day , No . 2 security official in Michoacan state , 3 others , shot to death . Mexico has seen wave of violence since president declared war on drug cartels .