Officials from the U.S. federal government have admitted to arresting, then releasing mere hours later, a man who admitted to manufacturing hundreds of improvised explosive devices for a Mexican drug cartel, according to a report in the Wall Street Journal. The man was arrested last week in Mexico, where authorities reportedly seized materials that could be used to manufacture 500 grenades.

The U.S. Attorney’s office in Phoenix, AZ, declined to charge Jean Baptiste Kingrey, the Wall Street Journal reported, despite the strenuous objections of at least one agent from the Bureau of Alcohol, Tobacco, Firearms and Explosives, who was leading the ATF’s investigation into the grenades case.

The U.S. Attorney’s office sought to enlist Kingrey as an informant against the La Familia Michoacana cartel. Kingrey “maintained contact with agents for several weeks,” according to the Journal, “then disappeared, the U.S. officials familiar with the case said.”

But while the ATF apparently insisted on charging Kingrey when he was arrested in June, the man was also part of an ATF operation earlier this year that involved allowing him to “walk” explosives over the U.S.-Mexico border as part of the Bureau’s efforts to investigate drug cartels, federal prosecutors claim. ATF agents hoped to track Kingrey’s movements, but apparently lost track of him before he arrived at the border, where Mexican authorities failed to prevent his entry.

The ATF operation appears to have taken place parallel to – and not an official part of – the Bureau’s Fast and Furious gun-running operation. But it bears some striking similarities to the scandalous operation that has come under fire since Border Patrol Agent Brian Terry was killed in the line of duty in December. Guns identified as part of that operation were found at the scene.

Peter Forcelli, the ATF agent who reportedly pushed to charge Kingrey when he was arrested in June, was also involved in Fast and Furious, and has testified before Congress on the botched operation. Forcelli claims that Justice Department officials authorized the Bureau’s attempt in February to track Kingrey across the border. “Agree [with] the course of action as the variables play out,” read one internal email from the U.S. attorney, according to the Journal.

Rep. Darrell Issa (R-CA), who has been leading the investigation into Fast and Furious from his post as chairman of the House Oversight and Government Reform Committee, issued a brief statement on the revelations regarding the ATF’s February operation, calling the information “disconcerting.”