MATAMOROS, Mexico (NewsNation) — A Mexican cartel claims to have turned over five of its own members who they say orchestrated Friday’s attack that left two Americans dead.

The men were purportedly left handcuffed by the Gulf Cartel with an apology note saying those responsible for killing the Americans would pay.

Drug cartels have been known to issue communiques to intimidate rivals and authorities, but also at times like these to do some public relations work to try to smooth over situations that could affect their businesses.

“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,” the letter reads, adding that those individuals had gone against the cartel’s rules, which include “respecting the life and well-being of the innocent.”

A photograph of five men facedown on the pavement and bound accompanied the letter, which was shared with NewsNation by a source on condition that the source remains anonymous.

State officials did not immediately publicly confirm having new suspects in custody.

Despite the perceived omission, Mexican authorities continued their search Thursday for those responsible for the kidnapping of four Americans in Matamoros, investigating a possible drug motive for the attack.

Latavia McGee and Eric James Williams survived the attack and have been receiving medical care in the U.S., while the bodies of Shaeed Woodard and Zindell Brown remain inside a state morgue in Mexico. Their remains are expected to be returned to the U.S. as soon as Thursday.

However, there are still questions about why those Americans were in Matamoros. The town is one of the most dangerous along the southern U.S. border, largely due to the ongoing war between the Gulf and Los Zetas cartels.

Initial reports claimed the Americans were traveling down to the area for a medical procedure. But new information has raised questions about a possible connection between the Americans and the kidnapping.

Mexican law enforcement agents said they were investigating the possibility that members of a drug cartel kidnapped the Americans thinking they were encroaching on their turf, according to an internal government document seen by Reuters.

Mexican officials, who said they are pursuing various lines of inquiry, drew up a brief document summarizing the abduction of the Americans and biographical information on them. The metadata of the digital document suggested it was created on Wednesday.

It included their names, birthdays and addresses, and details of criminal records. Among them were convictions against Brown and Woodard on drug-related charges.

In view of the prior convictions, “It cannot be ruled out that the attack against (the Americans) could be directly linked to drug trafficking operations,” which their assailants believed the Americans could be carrying out, the document said.

A Reuters review of South Carolina state records found that Woodard was convicted five times between 2007 and 2016 of drug crimes. Nearly all were minor offenses, but they included one of manufacturing banned narcotics with the intent to distribute.

Brown was convicted twice in 2015 for possessing small amounts of marijuana or concentrated cannabis, records show.

The records also showed that Williams was convicted in 2017 for the manufacture and distribution of cocaine, though this was not mentioned in the Mexican document seen by Reuters.

It was revealed that one of the survivors, Eric Williams, has a criminal history of distributing cocaine.

Tamaulipas Attorney General Irving Barrios told the same news conference the four were likely mistaken for somebody else while stressing that other lines of the investigation remain open.

Reuters could not ascertain how a drug gang might have known Americans with drug convictions were arriving in Matamoros.

Mexican sources told NewsNation that the Gulf Cartel is in charge of the region and has turned Matamoros into part of a key drug trafficking route for the distribution of cocaine.

There has been a large, heavy police presence since the incident. Two men were arrested earlier Wednesday in Matamoros and brought in for questioning. It’s unknown if those arrests are connected to the kidnapping case.

The Associated Press and Reuters contributed to this report.