Sept. 30, 2012 -- Fifty seven previously unidentified firearms linked to Operation Fast and Furious were recovered in sites associated with murders, kidnappings, and at least two gruesome massacres.

Univision News obtained the list of Fast and Furious weapons and a list containing almost 60,000 recovered firearms compiled by Mexico's Secretaría de la Defensa Nacional (SEDENA). A cross-reference of the serial numbers of the guns resulted in 96 full matches (several partial matches were discarded). The 96 firearms linked to Operation Fast and Furious all turned up at crime scenes in Mexico from 2009 to 2010.

In a report published on July 26, Congress mentioned there were "at least 48 recoveries involving 122 weapons [in Mexico] connected to Operation Fast and Furious." To check whether those were the same guns pinpointed by the data cross-reference, Univision News contacted congressional investigators asking for the serial numbers of the 122 guns in Congress' report. After an initial request by Univision News in mid-September and despite numerous phone calls and emails, there was no further response.

Univision News then gathered all the serial numbers available in the evidence appendixes of the major congressional investigation released by Rep. Darrell Issa (R-Calif.) and Iowa Senator Charles Grassley last July. Another data analysis showed that five of the weapons in the list of 96 were already mentioned in the hundreds of emails and the 4473 forms that the Department of Justice had given to Congress. (The 4473 forms, also known as Firearm Transaction Records, are the documents that people who are purchasing guns from a Federal Firearm Licensee must fill.)

A search of SEDENA's press releases, which often include the serial numbers of seized firearms, resulted in one more firearm whose serial number matched one of those already in Congress' list.

Finally, Univision News compared the recovery dates and locations highlighted in The Department of Justice's Operation Fast and Furious: Fueling Cartel Violence, with those found in the remaining list of 90 weapons. For the cross-reference list and Congress' list, we divided each year's recovered guns by state. After that, we compared the number of weapons found in each state on both lists. That is, we compared the number of guns recovered, say, in 2009 in Baja California, according to lists by Congress and by Univision News.

For instance, if Congress had identified seven Fast and Furious weapons recovered in Baja California in 2009, and our list mentioned 24, then we concluded that our list included at least 17 new weapons. In the end, the state-by-state analysis showed that 57 of the firearms in the cross-reference were not included in Congress' report.

Univision News started looking for unreported Fast and Weapons after discovering a SEDENA document, which said that three guns from an ATF gun-tracing operation were used in the massacre in Villas de Salvarcar, Ciudad Juarez.