"These documents have been the subject of requests by ranking members of Congress and litigants following the rendition of hundreds of Venezuelans and a small number of Salvadorans to the Salvadoran prison known as CECOT in March—the rendition of Venezuelans being effectuated under the purported wartime authority of the Alien Enemies Act.
The documents provide few additional details on the prisoner transfer arrangement between the United States and El Salvador—telling in its own right. Rather than memorializing the full terms of the deal, the principal function of these documents appears to be establishing a written record that the United States sought and received (and then sought to remind El Salvador of) assurances that detainees transferred to El Salvador would be treated humanely and not tortured, consistent with El Salvador’s obligations under the Convention Against Torture.
Seeking such assurances that foreign partners will not violate international law is a longstanding practice by the U.S. government—a practice of dubious value. Here it seems that State Department lawyers sought to create a paper trail in an attempt to rebut claims that the United States or U.S. officials renditioned people to El Salvador intent that they be abused—actions that could violate the United States’ own treaty obligations and potentially expose U.S. officials to criminal prosecution abroad. These documents should be understood as a legal fig leaf."
https://www.justsecurity.org/117271/us-elsalvador-diplomatic-notes/