( CNN ) -- On Sunday , Raquel and Pedro Alvarado buried three of their children -- Erica , Alex and Jose Angel -- in the Mexican village of El Control , just five miles south of the Texas border . The final resting place for the youths -- all in their 20s -- is the place where their family originated . But this small community , administered by the larger border city of Matamoros , merely provides bookends to the lives these three Americans had north of the Rio Grande . The siblings were born in the United States , grew up in Progreso , Texas , and continued to make their lives there . They disappeared on October 13 -- kidnapped , witnesses say -- as they returned to Texas from a trip to visit their father in El Control . Their bodies were found last week . Each was bound at their hands and feet , the Tamaulipas State Attorney General 's Office said , and each had a gunshot wound to the head . A fourth victim , Jose Castaneda , met the same fate . Castaneda was Erica 's boyfriend , her family said . All four were killed the same day they disappeared , a spokesman for the State Attorney General 's Office said , without elaborating . Some witnesses told investigators that the armed men who confronted and took the youths belonged to a new security force known as `` Grupo Hercules , '' State Attorney General Ismael Quintanilla Acosta told reporters . Grupo Hercules was created one month before the disappearance of the youths . It is touted as an elite security force under the direction of the mayor of Matamoros , 37-year-old Leticia Salazar . In parts of Mexico like this stretch of border , where drug cartels battle each other and law enforcement , things are n't always what they seem . Drug gangs have been known to pose as cops . Cops have been known to be on cartel payrolls . Cases of mistaken identity have had deadly consequences . But what troubles Pedro and Raquel Alvarado is that no one has offered a motive or theory about why their children and Castaneda were killed . No one has accused the Alvarado siblings of being involved in criminal activity . And while nine members of Grupo Hercules were interrogated by investigators , no arrests have been made . Salazar , the Matamoros mayor , has neither defended nor disciplined her security forces -- at least publicly . Contacted by CNN , Salazar referred questions to the city 's public affairs team , which earlier said it did not have any comment on the allegations against Grupo Hercules and could not confirm why the group was created or even its size . In a news release announcing the group 's unveiling , Grupo Hercules is described as being tasked with combating crime and made up of forces capable of carrying out intelligence and high-risk operations . A week ago , the attorney general said his investigators would call in the mayor for questioning , but that has not happened . `` I do n't know why they took them , '' Pedro Alvarado said . `` They did n't start trouble with anyone . They were quiet , not aggressive . '' If her children were mixed up in something criminal , there should be a record of their arrests or charges against them , but those are nonexistent , Raquel Alvarado said . `` If I knew they were doing something wrong , I would have recognized it as their mother , '' she said . `` And until someone proves otherwise , I will continue defending them . '' Pedro , Raquel 's former husband , was the one to identify the remains of his children , which were in an advanced state of decomposition , the State Attorney General 's Office said . He identified them by their clothing , shoes and some tattoos . The U.S. Consulate in Matamoros has been assisting the family . `` We have been in contact with Mexican officials both in Washington and in Mexico to find out further details of the case , and will take appropriate action ( if necessary ) once more is known about the circumstances , '' a State Department official said . An FBI spokeswoman said the agency is assisting Mexican officials with any part of the investigation on the U.S. side of the border . Three lives . The final Facebook post that Erica Alvarado shared -- at least publicly -- is a fitting , if unplanned , goodbye . It is a collage of photos of her four children atop a backdrop with the words `` I love you . '' She was born in Florida , and like her siblings , grew up in Progreso , a Texas town on the border and about as close as you can get to El Control on the U.S. side of the boundary . She was a dedicated mother , Pedro Alvarado said , and was planning to enroll in a nursing program . Her brother Alex loved his Chevy Tahoe , his father said . Alex 's social media postings reflect that : photos of the Tahoe muddied , photos after a paint job , the Tahoe as a profile picture . The same armed men who took his children took the Tahoe , Pedro Alvarado said . The 22-year-old had a prominent tattoo on his left arm -- an image of St. Jude , the saint of lost causes -- the father said . By now , Alex and his brother , Jose Angel , should have been in Missouri , doing seasonal agricultural work , Pedro Alvarado said . Jose Angel was born in Houston , and Alex in Harlingen , during Pedro 's own days as a seasonal migrant worker in the United States , their father said . Routine visit . The siblings visited their father in El Control each week , Pedro Alvarado said . On their short drive back to Texas , the Alvarado siblings stopped at `` La Curva Texas , '' a small restaurant underneath the last major overpass before the Los Indios International Bridge , Pedro Alvarado said . They arrived separately , Raquel Alvarado said . According to what witnesses have told her , Alex and Jose Angel arrived at the restaurant to find armed men beating up their sister and her boyfriend . The brothers intervened , and the armed men overpowered all four and placed hoods over their heads before escorting them away , the mother said . It was there , he said , that they were last seen before their bodies were found 16 days later . Raquel Alvarado said she and Pedro have told all this to authorities , but she accuses investigators of moving slowly . The facts that are known , she said , are thanks to the investigative work of Pedro , who tracked down witnesses . There was an outpouring of support at the funeral , Raquel Alvarado said . Family from across Texas and Mexico attended , and when the funeral procession moved from the church to the burial ground , they found that the crowd would n't fit in the cemetery . On Monday , the mother was back in Progreso , hoping to get some sleep to recover from the whirlwind of mourning , frustration and media spotlight . `` I hope when I wake up I will learn this was all a nightmare , '' she said . `` But I know it is n't . '' Mexican mayor , wife arrested in case of missing students . CNN 's Elwyn Lopez and Rosa Flores contributed to this report .
Three siblings from Texas , another man , went missing in Mexico on October 13 . Some witnesses say security forces took them . Erica , Alex and Jose Angel Alvarado , and a fourth person who was with them were found dead . They were buried Sunday in Mexico .