ACAPULCO, Mexico -- Forensic investigators searched for more hidden graves Thursday near where they had already found 18 badly decomposed cadavers that are suspected to belong to a group of Mexican tourists who were kidnapped in Acapulco.
Guarded by soldiers and marines, the investigators used long metal poles to probe the ground in a coconut palm grove in the community of Tuncingo, just east of Acapulco. An anonymous tip led police to the bodies of two men there on Wednesday.
Next to the bodies was a sign that said investigators would find the remains of 20 men -- most of them mechanics -- who vanished on Sept. 30 after setting out from the neighboring state of Michoacan for a few days off in Acapulco, a Pacific coast resort popular with Mexican tourists.
"We have not said that it is them, but we have not discounted that either," said David Sotelo, attorney general for the state of Guerrero, where Acapulco is located.
But he said he had asked officials in Michoacan "to put us in contact with the relatives of the people who were kidnapped so that they can identify whether the bodies are those of their relatives."
The Michoacan state government said in a statement that a group of relatives would be escorted to Acapulco on Saturday to view the bodies and that security would be provided for them.
Before the first two bodies were found, a video posted on YouTube showed two men -- their hands apparently tied behind their backs -- telling an unseen interrogator that they killed "the Michoacanos" and buried them in the area.
The two bodies found by police were wearing the same clothes as the pair seen in the video and were lying atop the mass grave.
A sign left between the two men read: "The people they killed are buried here." It was signed by Acapulco's Independent Cartel -- a little known drug gang that has been claiming responsibility for killings in the area over the past two months.
The group is believed to be a breakaway faction of the Beltran Leyva gang, whose top leaders have recently been killed or captured. The men interrogated in the video appear to be members of a rival faction.
In the video, the two men say the killing was an act of revenge against La Familia, a powerful drug cartel based in Michoacan. Officials have not said whether the abductors killed them merely because they were from Michoacan, or because they thought they were somehow linked to La Familia. Michoacan officials have said the disappeared men had no criminal records.
The families of the 20 missing men, many of them related to each other, have said they were mechanics in the Michoacan state capital of Morelia who saved up money to take a vacation together each year.
The kidnapping was one of the biggest blows yet to tourist-dependent Acapulco, which has seen an increase in drug-gang shootouts, beheadings and kidnappings. Even Acapulco Mayor Jose Luis Avila Sanchez recently urged residents to stay indoors after nightfall, an extraordinary pronouncement in a city where the economy is built on nightclubs, bars and restaurants.
In yet more violence Thursday, four city police officers in Acapulco were shot to death in two separate attacks, authorities said.
The officers were attacked while on patrol by gunmen traveling in luxury SUVs, Guerrero state's Public Safety Department said in a statement. A fifth officer was wounded when gunmen shot him while he directed traffic in the resort city.
Mass killings have become more frequent amid raging, drug-fueled violence in Mexico. In the most horrifying attack, 72 migrants were massacred in northern Mexico near the border city of Matamoros in August, apparently because they refused to work for the Zetas drug gang.
Cartels are increasingly releasing videos of kidnapped people admitting at gunpoint to crimes ranging from extortion to murder. It is often impossible to determine the veracity of confessions given under duress, and many of the victims are soon found dead.
One recent video showed the kidnapped brother of Patricia Gonzalez, the former attorney general of northern Chihuahua state, saying his sister protected a street gang tied to the Juarez cartel and was behind several murders.
He has not been found. Gonzalez denied any links to drug traffickers and said she is sure her brother spoke out of fear. On Thursday, the federal Attorney General's Office said it was opening an investigation into the case.