A Mexican cartel blamed for the kidnapping of four Americans last week appeared to issue an apology and turned over five of its own members to authorities for their alleged role in the abduction, according to a letter obtained by The Associated Press.

“We have decided to turn over those who were directly involved and responsible in the events, who at all times acted under their own decision-making and lack of discipline,” said the letter, which claimed to be from the Scorpions faction of the Gulf cartel, per the AP.

The letter was reportedly accompanied by a photo of five men bound and laying face-down on the pavement. One state official confirmed to the AP that five men had been found tied up inside a car with the letter.

The news outlet obtained the letter from a Tamaulipas state law enforcement official.

The four Americans were traveling to Mexico for a medical procedure last Friday when they were kidnapped by a group of armed men just after they crossed the border in Matamoros. Two were killed, one was injured and another remained unharmed. A Mexican citizen was also killed by a stray bullet.

The letter reflects a familiar tactic used by cartels in an effort to smooth over bad publicity that could impact its business, according to the AP.

The apparent letter from the cartel comes after Sen. Lindsey Graham (R-S.C.) said he was prepared to introduce legislation to “set the stage” for the U.S. to use force in Mexico.

“I would put Mexico on notice,” Graham said in an appearance on Fox News earlier this week. “If you continue to give safe haven to drug dealers, then you are an enemy of the United States.”

Mexican President Andrés Manuel López Obrador on Thursday slammed U.S. lawmakers for suggesting military action against Mexican drug cartels.

“We are not going to allow any foreign government to intervene, much less a foreign government’s armed forces,” López Obrador told reporters during a press conference.

“We are not a protectorate of the United States, nor a colony of the United States,” he added. “Mexico is a free, independent, sovereign state.”