“We have decided to extradite those directly involved and responsible in the events, who at all times acted according to their own decision-making and lack of discipline,” the letter reads, adding that those individuals had gone against the rules of the cartel . including “respect for the life and well-being of the innocent”.

Drug cartels have been known to issue communiqués to intimidate rivals and authorities, as well as times like these when public relations work to smooth over situations that could affect their business. And last Friday’s violence in Matamoros was bad for cartel business.

The Americans’ killings brought National Guard troops and an Army special forces unit leading patrols that “warm up the square” in narco terminology, Mexican security analyst David Saucedo said.

“It is very difficult for them right now to continue working in the field of street drug sales and drug transfer to the United States; they are the first to be interested in closing this chapter as soon as possible,” said Saucedo.

A photo of five men bound face down on the sidewalk accompanied the letter, which the official shared with The Associated Press on the condition that they remain anonymous as they were not authorized to share the document.

State officials did not immediately publicly confirm that new suspects had been taken into custody.

A separate state security official said five men were found tied up in one of the vehicles authorities were searching for, along with the letter. That official also spoke on condition of anonymity because they were not authorized to speak about the matter.

The nephew of one of the victims said his family feels “great” knowing Eric Williams, who was shot in the left leg, is alive, but won’t accept an apology from the cartel blamed for kidnapping the Americans.

“It won’t change the suffering we’ve been through,” Jerry Wallace told the AP on Thursday. Wallace, 62, called on the US and Mexican governments to better crack down on cartel violence.

Last Friday, the four Americans crossed from Texas to Matamoros so that one of them could undergo cosmetic surgery. Around noon they were fired upon in the center of Matamoros and then loaded into a pickup truck. A Mexican woman, Areli Pablo Servando, 33, was also killed, apparently by a stray bullet.

Another friend, who remained in Brownsville, called police after he couldn’t reach the group crossing the border Friday morning.

Brownsville Police Department spokesman Martin Sandoval said Thursday that officers were following protocol by checking local hospitals and jails after receiving the missing persons report. Within an hour, a detective was assigned to the case and then alerted the FBI after realizing the people had entered Mexico. Soon after, the FBI took over the case when videos on social media began to show a shootout with the casualties matching the description of the missing persons.

Authorities located them on the outskirts of the city on Tuesday morning, guarded by an arrested man. Zindell Brown and Shaeed Woodard were killed in the attack; Williams and Letavia McGee survived.

On Thursday, two hearses carrying the bodies of Woodard and Brown crossed the international bridge to Brownsville, where the remains were handed over to US authorities.

Woodard’s cousin, McGee, had surprised him with the fatal road trip as a birthday getaway, according to his father, James Woodard. He said he was speechless when he learned that the cartel had apologized for the violent kidnapping that killed his son and was captured in footage that quickly spread online.

“Just being helpless — not being able to do anything, not being able to go there to rescue them — it’s really painful,” James Woodard said.

Thursday’s letter was not an unheard-of cartel tactic.

The community relations efforts of cartels are well known in Mexico. In disputed territory, a cartel may hang banners around a city to blame a rival for the recent violence and distinguish itself as the gang that doesn’t mess with civilians.

Last November, such banners appeared in the state of Guanajuato, allegedly written by the Jalisco New Generation cartel, blaming a rival for a spate of murders at bars and other businesses.

In other situations, the message is more blunt: bodies are left in a vehicle with a note or hanged from a highway overpass on a busy road. The motivation is terror.

More subtle, cartels use their power to plant stories in the local press or prevent stories from appearing. Their members are active on social media.

Their underlying interest is facilitating their affairs, whether that be drug smuggling and migrants or extortion.

Sometimes a cartel invades its rival’s territory in the hopes of sparking a law enforcement action to make things difficult for their opponents’ business. That seemed to happen two years ago in Reynosa, just on the border of Matamoros. Gunmen drove into town firing and killed 14 innocent bystanders.

The handing over of suspected cartel suspects to the police is also not without precedent. Saucedo warned that a cartel leader might have authorized the attack, regretted it and decided to offer sacrificial lambs to the police.

In 2008, drug traffickers in Michoacan threw hand grenades into a crowd celebrating Mexico’s independence, killing eight. Days later, authorities arrested three suspects, but it turned out they had been kidnapped by a cartel, beaten into confessions involving a rival group, and handed over to the police.

Meanwhile, the Tamaulipas prosecutor’s office said on Thursday it had seized an ambulance and a medical clinic in Matamoros that were allegedly used to treat the Americans after the shooting.

The Americans told investigators they were taken to the clinic in an ambulance to receive first aid, the statement said. By reviewing police surveillance videos in the city, authorities were able to identify the ambulance and locate the clinic. According to the statement, no arrests have been made at the clinic.

Stevenson reported from Mexico City and Pollard from Lake City, South Carolina. Associated Press writer Acacia Coronado in Austin, Texas, and Associated Press videojournalist Hilary Powell in Lake City, South Carolina, contributed to this report.