Three US citizens last seen with police in Mexico are found dead Three US citizens who were in Mexico visiting their father and were last seen in the custody of police have been killed along with a friend, authorities said Friday. Their bodies, each with a gunshot to the head, have been identified by relatives, authorities in the border state of Tamaulipas said. Two brothers, their sister and her boyfriend were killed after being taken away by an ad hoc police force in the city of Matamoros, authorities and relatives said. The police force, known as the Hercules squad, was seen taking the three men and the woman away, witnesses said. The Hercules police force is an elite group formed by the mayor of Matamoros, Leticia Salazar, according to the Tamaulipas prosecutors' office. Some officials in the most conflict-ridden parts of Mexico have formed their own security squads as a way to protect themselves when they cannot trust often-corrupt police. The siblings' father, Pedro Alvarado, said he searched high and low when the four went missing but was unable to find them, until he was called to the morgue on Thursday. "They were coming back, stopped to eat at a place called Roasted Meat Curve, and from there they got taken away," Alvarado told reporters. I went looking for them in Matamoros and they didn't turn up, until just yesterday, I identified the bodies. Dozens of Americans, most with family in Mexico, have been killed or gone missing. US State Department advisories urge Americans to avoid many parts of Mexico - Tamaulipas is one of the principal danger zones - because of killings and kidnappings. Alvarado said he had yet to give DNA samples to confirm the identity of his children, all of whom lived in Texas. "The bodies are not recognizable, you can't see anything, not the face, just the clothes," he said, adding that teeth would be used to make a definitive identification. His preliminary identification was based on pictures of tattoos that officials showed him, as well as the clothing. The dead were identified as Erica Alvarado Rivera, 26; her brothers, Alex, 22, and Jose Angel, 21; and her boyfriend, Jose Guadalupe Castaneda, 32. They disappeared on October 13. Nine members of the Hercules police force are being questioned in connection with the deaths, The Associated Press reported. "We will apply the full force of the law and zero tolerance," Tamaulipas Governor Egidio Torre Cantu said. This would be the third case this year of suspected extrajudicial killing by Mexican security forces, following the army's slaying this year of 22 gang members, after they had surrendered, and the disappearance of 43 college students last seen a month ago being taken away by local police. Los Angeles Times