MS-13 is the gang that has the FBI most worried
Mara Salvatrucha is perhaps the most dangerous gang in the country at this point. Originating in El Salvador, the gang has gone transnational, with members across the United States (in 42 states) and in countries like Guatemala and Mexico.
MS-13 has worked with Mexican drug cartels and communicates frequently with incarcerated members despite no official leadership structure.
The gang is notoriously violent, relentlessly cruel and merciless, with plenty of well-documented public crimes, such as a San Francisco member who killed a family for briefly blocking his car. . .
Read more: http://www.businessinsider.com/dangerous-american-gangs-fbi-2011-11?op=1#ixzz3Tw1c3oEx