TUCSON, Ariz. (AP) — Authorities made a rare disclosure Monday linked to the botched gun-smuggling investigation known as Operation Fast and Furious, revealing the identities of four men accused of involvement in the shooting death of a U.S. Border Patrol agent 18 months ago.

The announcement comes in the wake of pressure from U.S. House Republicans who led a vote to hold Attorney General Eric Holder in contempt of Congress, criticizing the nation's top prosecutor for withholding information related to the probe.

Operation Fast and Furious was launched in 2009 to catch trafficking kingpins, but federal agents lost track of many weapons they were trying to trace.