Karl also claimed Montano was involved in the conspiracy behind the 1989 killing of six Jesuit priests, their housekeeper and her daughter.
Woodlock ordered Montano to respond by March 1 to Karl's report.
"Irrespective of what the government agreed to or didn't agree to … the allegations concerning Mr. Montano's activities with the military are matters that would cause me to consider an upward departure or variance," Woodlock said.
Woodlock added that he considers Karl's affidavit "evidence that the defendant is free to rebut or not as he sees fit."
In addition, Woodlock said he'd consider letters he received by the human rights organization the Center for Justice and Accountability evidentiary "if the government presses me."
"We're not seeking to prove the substantive charges he may have faced in Salvador -- just that he was seeking to come here to avoid prosecution," said Assistant U.S. Attorney John Capin.
Montano's lawyer, Oscar Cruz Jr., an assistant federal defender in Boston, said the individuals who sent the letters "are not quote unquote the victims" of the immigration offense.
Woodlock also gave the government until March 1 to address issues raised by the First Circuit case, U.S. v. Canada, cited in Montano's filing, which involved a prosecutor's "implied repudiation of the government's bargain."
Montano's January 14 response to the government's sentencing memorandum stated that the government's submission of "highly inflammatory information," including the Karl report, violates the plea agreement.
Woodlock said he sees a problem with the Canada case's suggestion that the government "must stand mute" on its plea recommendation even if facts and circumstances arise out of the presentencing report or the judge's inquiry that would support a different sentence.
Woodlock also ordered the parties to brief him on two other issues. One is the significance he should give the defendant's efforts to seek a Salvadoran passport during the proceedings. The other is whether the government intends to honor a pending extradition request by Spain for the defendant during his incarceration.