FBI issues reward for Fast and Furious murder
The FBI has offered a $1m (£644,000) reward for information on four suspects wanted over the killing of a US border patrol agent in December 2010.
In an indictment issued on Monday in Arizona, the men are accused of murdering Brian Terry.
Two firearms found at the crime scene went missing in the botched gun-running operation known as Fast and Furious.
A congressional inquiry into the matter led to a historic contempt vote against the US attorney general last month.
The FBI named the four fugitives as Mexicans Jesus Rosario Favela-Astorga, Ivan Soto-Barraza, Heraclio Osorio-Arellanes, and Lionel Portillo-Meza, whose nationality was not given.
A fifth suspect, Manuel Osorio-Arellanes, has been in custody since the night of the shooting on 12 December 2010, said a statement by the Department of Justice .
He was shot during the gunfight that led to the death of Terry, a former marine and Michigan police officer.
"Agent Terry served his country honourably and made the ultimate sacrifice in trying to protect it from harm, and we will stop at nothing to bring those responsible for his murder to justice," said Attorney General Eric Holder.
As well as murder, the suspects are charged with assaulting four federal agents.
The five men, plus another who faces lesser charges in the case, came to the US from Mexico in order to rob cannabis smugglers, according to the indictment.
The Department of Justice said last month that it would not prosecute the attorney general over his refusal to hand over to Congress documents on the bungled gun-running operation.
Their statement followed a vote by lawmakers in the House of Representatives to hold the US government's top justice official in contempt.
Launched in 2009 in Arizona by agents of the Bureau of Alcohol, Tobacco, Firearms and Explosives, Fast and Furious was a sting operation designed to track weapons smuggled to Mexican drug cartels.
But hundreds of the illegal guns went missing.