Federal authorities are still investigating the murders of a woman and three of her grandchildren on the Mandan, Hidatsa and Arikara Nation in North Dakota.

Martha Johnson, 63, and her grandchildren Benjamin Schuster, 13, Julia Schuster, 10, and Luke Schuster, 6, were shot and killed at her home on the reservation on November 18, 2012. The suspected assailant, Kalcie Eagle, 21, killed himself while being questioned by police.

Murder charges aren't pending but U.S. Attorney Tim Purdon said other charges are possible. “We want a thorough investigation, not a quick one," he told The Bismarck Tribune.

Get the Story:
U.S. attorney says New Town deserves to know the full story about murders (The Bismarck Tribune 2/14)

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Woman and grandchildren killed on North Dakota reservation (11/19)