Kaare Rodahl, a scientist with the US Air Force's Arctic Aeromedical Laboratory, spent much of the 1950s traveling to villages in the Alaskan Arctic to conduct research on cold acclimatization. Four decades later, it was discovered that during one such study, he had administered radioactive isotopes of iodine-131 to over one hundred Alaska Native research subjects without their knowledge or consent. This news broke just as Alaska Native communities were attempting to recover from a series of revelations surrounding other instances of Cold War radiation exposure. In response, two major federal investigations attempted to determine whether Rodahl had adhered to ethical regulations and whether his actions could be expected to have a lasting health impact on former research subjects. The National Research Council, framing the study as a singular event in the Cold War past, found that research subjects had been 'wronged, but not harmed'. The North Slope Borough, a powerful Alaska Native municipal government, countered this finding with their own investigation, which identified both the study and the subsequent federal inquiries as facets of the still-unfolding process of American settler colonialism in Alaska. In doing so, the North Slope Borough contested the authority of federal agencies to set the terms by which ethics could be retrospectively judged. This article argues that exploring how competing ethical regimes represent the relationship between violence and time can help us better understand how institutionalized bioethics reproduces settler colonial power relations.