The ACLU has filed suit over the deaths in drone strikes of three U.S. citizens: Anwar Al-Aulaqi, his 16-year-old son, and AQAP propagandist Samir Khan. The complaint is available here. The ACLU's press release is available here. I haven't yet read the complaint, which just became available a few moments ago, but Hina Shamsi, director of the ACLU's National Security Project, says the following in an email:
Our lawsuit, which is against senior CIA and military officials, charges that the killings of U.S. citizens Anwar Al-Aulaqi, Samir Khan, and 16-year-old Abdulrahman Al-Aulaqi in Yemen last year violated the Constitution’s guarantee against the deprivation of life without due process of law.
We argue that since 2002, and routinely since 2009, the United States has carried out deliberate and premeditated killings of suspected terrorists overseas, outside the context of armed conflict, based on vague legal standards, a closed executive process, and evidence never presented to the courts.
Our lawsuit says that outside of armed conflict, both the Constitution and international law prohibit targeted killing except as a last resort to avert a concrete, specific, and imminent threat of death or serious physical injury. Even in the context of an armed conflict against an armed group (which we don’t think existed in Yemen at the time of these killings), the government may use lethal force only against individuals who are directly participating in hostilities against the United States. We note that the concept of “direct participation” requires both a causal and temporal nexus to hostilities. In addition, regardless of the context, whenever the government uses lethal force, it must take all possible steps to avoid harming civilian bystanders. The lawsuit alleges that the senior CIA and military leaders who authorized and directed the killings at issue violated these standards.