Murillo, known as Don Berna, took control of the drug trade around Medellin after the death of fabled drug kingpin Pablo Escobar. He is now in a Colombian jail, and U.S. authorities are seeking his extradition.
In an interview, U.S. officials who spoke on condition of anonymity said they have closely investigated whether Uribe himself has collaborated with the right-wing paramilitaries in illegal activities and have so far found no proof that he has. But they emphasized that they also could not rule it out.
One of the officials said that it would have been "unusual" for Uribe to be personally involved in the details of a military activity such as Operation Orion, even though the president conceived the campaign. "You don't see him typically involved in that sort of detail," the official said.
One longtime Colombia analyst, Adam Isacson of the Center for International Policy, a Washington think tank, said that any collaboration between Montoya and paramilitaries "would bring the army right into the heart of the scandal." U.S. and Colombian officials have insisted that any links between the Colombian military and the militias involved only low-level, renegade officers.
Already, eight members of the Colombian Congress have been jailed in the scandal, and the foreign minister, a close Uribe ally, has been forced to resign. Colombia's former secret police chief, Jorge Noguera, was arrested last month for allegedly giving paramilitary leaders information on left-wing labor organizers, some of them later killed. He was released Friday on a procedural issue but is subject to rearrest, government officials said.
At a news conference in Bogota, the capital, during his visit this month, Bush expressed confidence that Uribe's government could carry out a thorough investigation of the ties between officials and the paramilitaries.
"I support a plan that says that there be an independent judiciary analyzing every charge brought forth, and when someone is found guilty, there's punishment," Bush said. He said Uribe supported the same approach. Bush administration officials say Uribe deserves credit for being willing to seek the truth about the growing scandal.
Many Democrats in Washington have been less confident. Sen. Patrick J. Leahy, (D-Vt.) has argued that the scandal shows the need for a reassessment of U.S. support for Uribe. Many in Congress have contended that if aid to Colombia is not cut, it should at least be shifted so that more goes to non-military purposes.
One of the U.S. officials interviewed said there were signs that the scandal would be increasingly focusing on the military, including Montoya.
"A lot of people in the political class are very nervous," he said.
paul.richter@latimes.com
greg.miller@latimes.com
