In 1990, she was stabbed to death by elements in the Guatemalan military due to her criticism of the Guatemala government's treatment of the indigenous Maya, and human rights abuses against the people in general.
Due to her sister's pursuit of justice, Mack's killer was convicted and upper-level superiors tried in precedent-setting cases before the Inter-American Court of Human Rights in Costa Rica.
She was stabbed 27 times by an armed forces death squad (allegedly trained at the School of the Americas) because she had criticized the government for its human rights abuses of the indigenous communities.
In April 2004, following the judgment issued by the Inter-American Court of Human Rights, the Guatemalan government publicly acknowledged that its agents had committed the killing of Myrna Mack.
Her sister, Helen, was honored with a Right Livelihood Award in 1992 "for her personal courage and persistence in seeking justice and an end to the impunity of political murderers.