Carlos Gutierrez, 34, was arrested near the border with El Salvador after investigators traced over 60 telephone calls between him and the suspected killers, public prosecutor Alvaro Matus told reporters.

The charred and bullet-riddled bodies of three Salvadoran members of the Central American parliament and their driver were found abandoned at the end of a dirt track last Feb. 19.

Days later, four Guatemalan policemen were arrested for the crime, tracked to the scene by a satellite positioning system in their car. The policemen were then murdered inside a maximum security prison.

Investigators had said they knew the identity of "Montana 3," a code name used by Gutierrez during his phone calls with the suspected killers, but did not publicly identify him or detain him until now.

"He will be transferred to the capital under heavy security," Matus said. He gave no more details about Gutierrez.

The murders shed light on illegal armed groups within Guatemala's security forces and possible links between high-level officials and drug traffickers in Guatemala and El Salvador. Both countries are used to smuggle cocaine from South America through to Mexico and the United States.

Investigators say "Montana 3" had several telephone conversations with Manuel Castillo, an independent member of Congress recently elected to be mayor of the town of Jutiapa in a region police say is dominated by drug smugglers.

Guatemala's Supreme Court this week stripped Castillo of immunity he would have enjoyed as mayor, clearing the way for possible charges against him in connection with the murders.

But police say they cannot find Castillo, who has been accused in local media of having links to drug traffickers. (Reporting by Herbert Hernandez, Writing by Mica Rosenberg; Editing by Kieran Murray)