An operation headed by the Bureau of Alcohol, Tobacco
and Firearms, started in 2009. The ATF thought rather than arresting gun smugglers, they'd let the guns
roam free like cattle, allowing smuggling to continue, gambling it would lead them to cartel bosses. Instead they lost track of over
which has been been linked to numerous murders
in the US and Mexico.
This failure of an operation ironically later led to the deaths of US Border
Patrol and and ATF agents.