Violence in Mexico has increased since Congress allowed the federal assault weapons ban to expire in 2004.
Except it hasn't. From the AP:
Mexico's homicide rate has fallen steadily from a high in 1997 of 17 per 100,000 people to 14 per 100,000 in 2009, a year marked by an unprecedented spate of drug slayings concentrated in a few states and cities, Public Safety Secretary Genaro Garcia Luna said. The national rate hit a low of 10 per 100,000 people in 2007, according to government figures compiled by the independent Citizens' Institute for Crime Studies.