A U.S. federal judge dismissed a key charge against one of two men accused in the 1975 slaying of a Canadian aboriginal activist and scheduled a hearing on whether they should be tried separately.

John Graham, a Canadian man from the Tsimshian Tribe in the Yukon, and Richard Marshall, a Lakota Indian from the Pine Ridge reservation in South Dakota, are to stand trial starting May 12 in Rapid City, S.D.

They are facing federal charges, including murder and aiding and abetting the murder of Anna Mae Pictou-Aquash, a Mi'kmaq Indian from Nova Scotia shot to death on the Pine Ridge Indian reservation in 1975.

Like Graham and Marshall, Pictou-Aquash was active in the American Indian Movement (AIM), a militant U.S.-based group that advocates for aboriginal rights and was behind the 1973 standoff with government troops at the South Dakota village of Wounded Knee, where Sioux Indians were massacred by the U.S. cavalry in 1890. Prosecutors believe she was killed because fellow AIM members suspected she was a government informant.

Marshall was indicted in connection with her death in August, five years after Graham and another Lakota Indian from South Dakota, Arlo Looking Cloud, were charged.

Looking Cloud, who was living in Denver, was convicted in 2004 for his role in Pictou-Aquash's death and sentenced to life in prison. He's now a government witness.

Days before Graham's trial was to start in October, U.S. District Judge Lawrence Piersol threw out the indictment because it didn't show that either Graham or Pictou-Aquash belonged to a federally recognized American Indian tribe. Tribal status gives the federal U.S. government jurisdiction in the case.

In other words, Graham is a Canadian Indian and Pictou-Aquash was a Canadian Indian, so neither fit the definition of American Indian.

Graham had been living in B.C. and spent more than four years fighting his extradition to the U.S. before finally being deported in December 2007.

Federal prosecutors re-indicted Graham and Marshall, combined their cases and appealed Piersol's ruling. A three-judge panel with the 8th U.S. Circuit Court of appeals in St. Louis, Mo., heard oral arguments on the appeal April 15 but hasn't announced a decision.

Other 2 charges against Graham likely to be dismissed

Piersol has filed an order dismissing the third count against Graham in the new indictment — which is similar to the 2003 charge — which means prosecutors must prove to jurors that either Graham or Pictou-Aquash was part Indian.

Otherwise, the other two remaining charges against Graham will likely be dismissed, though the state of South Dakota could try him, Piersol wrote in his order.

Federal prosecutors argued that because Looking Cloud is Lakota, Graham can be charged as an aider and abetter. But Marshall's lawyer disputed that, saying federal law requires both to be a member of a federally recognized tribe.

Piersol agreed.

"There is no authority for this proposition, and the court rejects it," he said.

U.S. Attorney Marty Jackley said late Thursday he appealed the dismissal of the third count to a federal appeals court.

Piersol wrote that "considering the likelihood" the other two charges against Graham will be dismissed at trial, he wants lawyers to be ready to discuss whether the Graham and Marshall cases should be split, which both defence lawyers want.

Piersol scheduled a hearing for Tuesday in Rapid City to deal with it and other motions.

Graham's lawyer, John Murphy, filed a response late Thursday saying if the cases are split, he wants Graham — not Marshall — to go to trial first. Either way, he would be ready May 12, it states.

Piersol will also hear arguments on a request by Marshall to dismiss the indictment because the government waited 33 years to charge him. However, the judge wrote in an order that it does not appear prosecutors recklessly or intentionally delayed the charge.

Another request by Marshall is to prevent a government witness from testifying about a comment attributed to Marshall but one he denies making regarding whether Pictou-Aquash was tied up at his house the night she was killed.

The prosecution theory is that Marshall gave a .32-calibre revolver and shells to Graham, Looking Cloud and another AIM member, Theda Clarke, when they stopped by Marshall's house with Pictou-Aquash. Hours later, the prosecution alleges, Graham shot Pictou-Aquash because AIM leaders suspected her of being a government informant.

Clarke, who lives in a nursing home in western Nebraska, has not been charged, though prosecutors plan to call her as a witness.