PHARR, Texas (Border Report) — In the days following the kidnapping of four Americans — and deaths of two — in the Mexican border town of Matamoros, intelligence officers from the U.S. surveilled Mexican drug cartels, according to leaked classified documents reviewed by The Washington Post.

According to the Post, the transnational criminal organizations prepared for retaliation from Mexican security forces, and lawyers for the groups also urged cartel members to delete information regarding the Americans from their phones.

The leaked documents are part of dozens of classified military files and U.S. intelligence documents that the instant messaging social platform Discord, which is popular with online gamers, got a hold of last month.

Massachusetts Air National Guardsman Jack Teixeira, 21, was charged Friday in U.S. District Court in Boston with unauthorized removal and retention of classified and national defense information — a breach that has caused an international uproar and exposed explicit U.S. assessments on the war in Ukraine and other closely held secrets, the Associated Press reports.

The Post says it reviewed about 300 photos of the classified documents, most relating to the Russian war in Ukraine. But also included some intelligence data on U.S./Mexico relations, including that more violence could occur in the border town of Matamoros, south of Brownsville, Texas, “where the U.S. maintains a consulate,” according to The Post.

Border Report has not reviewed the classified documents.

The Post reported that the leaked information included communications between Gulf Cartel members indicating the group had turned the four Americans — including two who had died — over to Mexican authorities. The intelligence indicated the two were alive when they were taken after cartel gunmen fired upon their van.

Widely circulated video shows Shaeed Woodard and Zindell Brown shot on March 3 in Matamoros and heaved into the back of a truck along with Latavia “Tay” McGee and Eric James. All had traveled from South Carolina, they said, so that McGee, 34, could get plastic surgery in Matamoros.

According to Mexican investigative documents viewed by The Associated Press, authorities found McGee and James blindfolded in a shack on May 6 outside downtown Matamoros. Beside them were the bodies of Woodard and Brown, wrapped in blankets and plastic bags.

Leaked files indicate U.S. authorities were monitoring the kidnapping situation via possible wiretaps, according to the Post.

On Friday, McGee was arrested in Myrtle Beach, South Carolina, and charged with contributing to the delinquency of a minor, records show. The warrant alleges that she knowingly took her child to the location of a fight among youth.

The U.S. State Department warns Americans not to travel to the Mexican state of Tamaulipas, where Matamoros is located, “due to crime and kidnapping.”