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 2,000 guns 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.
Gun smuggler 1: Yo, that Fast and Furious thing was great. It made millions.
Gun smuggler 2: You mean that movie?
Gun smuggler 1: No, that stupid plan to get cartel bosses off the street. They let me to sell this 9mm to the guy down the street in hopes it would lead them to 'bigger fish'