Amnesty International has zeroed in on Cravath, Swaine & Moore, claiming in a Sept. 8 release that the New York firm is refusing to hand over “critical” evidence in long-running litigation against the oil giant Royal Dutch Shell.

Esther Kiobel, the widow of a Nigerian dissident who was executed by his country’s government in the 1990s, wants to hold Shell and its Nigerian subsidiary responsible for alleged human rights abuses in Nigeria’s Ogoni region. The U.S. Supreme Court dismissed a class action brought by Kiobel and others against Shell four years ago, finding that the case dealt with overseas conduct that was beyond the reach of the U.S. alien tort statute.