Mexico City ( CNN ) -- What happened to 12 youths who were kidnapped in broad daylight from a bar in Mexico ? The mystery , which has jolted the country 's capital for months , appeared to be one step closer to resolution Monday : . The victims were killed shortly after the kidnapping , Mexico City Prosecutor Rodolfo Rios Garza told reporters on Monday . And the motive was revenge , he said . The crime occurred in retaliation for another killing at a bar in the city 's upscale Condesa neighborhood , he said . The prosecutor 's revelation comes a day after an attorney representing victims ' families said authorities had found that at least 10 of the bodies discovered last week in a shallow grave near Mexico City corresponded to the group kidnapped from the Heaven after-hours club . The mysterious mass kidnapping in Mexico 's capital in May drew international attention after furious family members protested , claiming authorities were n't taking the case seriously . The allegations have sparked concerns about whether violence has surged into Mexico 's capital , where residents largely have been spared from drug war casualties seen in other parts of the country . Prosecutor : 'We are not talking about any cartel ' Rios said Monday that the group behind the kidnapping was La Union de Insurgentes , which has been tied to drug distribution in the capital . But he dismissed concerns about larger forces at work . `` We are not talking about any cartel , '' he said . But even with the new information released by authorities , victims ' family members said their outrage over the case has n't dimmed . One stood in the doorway of Monday 's press conference , wearing a T-shirt emblazoned with all 12 victims ' faces . As officials tried to get her to move , Julieta Gonzalez told them , `` I am not moving from here . I am not going to do anything . I only want to hear . '' Gonzalez -- whose daughter , Jennifer Robles , was among those taken from the bar -- said she wanted to listen because authorities have consistently given reporters details about the case before telling family members . Seven suspects arrested . Mexico 's Attorney General 's Office said Sunday that at least 10 of the remains found correspond to the kidnapped youths , attorney Ricardo Martinez told CNNMexico . Officials have not provided details about three other bodies found in the grave . Authorities found the grave last week in the town of Tlalmanalco , in the state of Mexico , about 30 miles east of Mexico City , the state-run Notimex news agency reported . Investigators have n't said what led them to the grave . Authorities have arrested seven suspects in connection with the crime , Rios said Monday . The owner of the bar , a co-owner and two bar employees are among those who have been arrested in the case . A suspect detained at a hotel in Mexico City last week told authorities he and others had taken the victims to Tlalmanalco , Rios said . `` We will not stop until we have achieved the detention of the rest of the participants in these events , '' he said , describing what he said had been an exhaustive investigation . Families call for independent investigation . But the mother of at least one of the victims said she was far from satisfied with the investigation so far , and wants more proof about what investigators exhumed from the grave last week . `` No one is sure of what is there . We have not seen clothes . They have not shown us bodies . They have not shown us anything , '' mother Leticia Ponce told CNN en EspaÃ±ol Monday . Victims ' family members have said they do n't trust Mexican authorities and have called for an independent international investigation of the case . `` I have always distrusted them . ... They have not shown me a hair or a nail from my daughter . I am not taking anything until they prove to me that it is my daughter , '' Gonzalez said . `` They are staging it . '' CNNMexico 's Veronica Diaz Favela and Arturo Ascencion , CNN 's Catherine E. Shoichet , journalist Nick Parker and CNN en EspaÃ±ol 's Mario Gonzalez contributed to this report .
NEW : One victim 's mother accuses authorities of staging arrests . Mexico City 's prosecutor says 12 kidnapped teens were killed . The motive was revenge , Mexico City 's prosecutor tells reporters . The teens ' kidnapping in broad daylight has jolted Mexico 's capital .