Authorities dug up a mass grave near Mexico City on Thursday and were investigating if the remains are those of 12 young people whose kidnapping in May shocked the capital. Mexico City\'s top prosecutor, Rodolfo Rios, said seven people\'s remains have already been recovered since the search began in a park on Wednesday and that workers are still digging for more bodies. The mass grave was discovered at the Rancho La Mesa ecological park in the municipality of Tlalmanalco, a mountain area of pine trees, corn fields and humble rural homes 30 kilometers (19 miles) southeast of the capital. A federal police officer at the scene told AFP that authorities had searched a ranch for weapons on Wednesday and found firearms in a parked trailer when they happened to find a stretch of land covered in cement. \"We began to dig and found the bodies,\" he said. The kidnapped, aged 16 to 34, were taken from a downtown bar in broad daylight on a Sunday morning three months ago in a case that raised concerns about security in Mexico City, challenging the perception that it is relatively immune from the country\'s drug cartel violence. Police put up a checkpoint on a dirt road surrounded by corn fields more than one kilometer from the mass grave to block access. Some relatives of victims were there with an attorney and one woman was seen sobbing, but the families refused to speak to reporters. \"For the moment seven bodies have been found in a pit,\" Rios told a news conference, stressing that it would take at least two days to get results from DNA tests to identify the victims. An official from the federal attorney general\'s office told AFP that the remains were mere bones, making it difficult for now to determine if they are male or female or the cause of death. A lawyer representing some victims\' relatives, Ricardo Martinez, said a police officer who was at the site told him that 13 bodies were found after the two detainees took authorities to the grave. \"According to the people who spoke with me and others I spoke with, I wouldn\'t doubt that it is them (the kidnap victims),\" Martinez told Milenio television. Rios said two people who live near the site were detained, but Attorney General Jesus Murillo Karam denied that anybody was held and also said that the discovery was made during a guns search. Rios has linked the mass kidnapping to a dispute between two gangs known as La Union and Tepis, which sell drugs in the city\'s rough Tepito neighborhood. But Mexico City Mayor Miguel Angel Mancera has insisted that the bigger cartels do not operate in the capital and initially classified the disappearances as a missing persons case. Mass kidnappings and murders are more common near the US border and western states. The former Mexico City police chief, Manuel Mondragon y Kalb, who now heads the federal police, said last month that the country\'s main gangs have \"crystalized\" in some areas of the capital. Most of those abducted hail from Tepito and two of them, including 16-year-old Jerzy Ortiz, are sons of jailed criminals. But their families insist that the youngsters are not involved in criminal activities. The group was whisked away by 17 men who walked into the Heaven bar on May 26 and put them in several cars, just blocks away from the federal police headquarters and the US embassy, officials said. Two bar owners have been arrested while the charred remains of a third associate was found in the central state of Morelos last month. Rios met with relatives of victims before his news conference. Earlier Jerzy\'s aunt, Eugenia Ponce Ramos, told AFP that Rios had telephoned the families and told them that authorities have yet to identify the remains. \"We have to stay calm,\" said Ponce, who is among scores of family members who have held protests in the capital to demand answers.