Homestead - Jose Amaya Guardado's mother said she brought her son to the US nine years ago to escape the violence rampant in their native El Salvador. But now his family is mourning his death in what police describe as a brutal machete attack.Miami-Dade police have charged four of Amaya Guardado's classmates with second-degree murder: Kaheem Arbelo, 20; Jonathan Lucas, 18; Christian Colon, 19; and Desiray Strickland, 18. Detectives said they're expecting to make a fifth arrest."I brought my son from there because they were killing people," Lucia Guardado said in Spanish at the family's south Miami-Dade home. "I never imagined they would do something like that to my son here."According to an arrest report, the suspects had planned the attack two weeks in advance.The report accuses them of luring Amaya Guardado, 17, to a wooded area near Homestead Job Corps, a live-in school and vocational training program for at-risk students run by the US Department of Labour. That's where Amaya Guardado was hacked to death with a machete and left in a shallow grave that the suspects had dug in advance, police said.Family members began searching for Amaya Guardado after he went missing 28 June. His brother discovered his body a few days later.Bullying gone brutalAmaya Guardado's father, Santos Amaya, said his son began attending the school months before his death. Amaya said his son - the youngest of six siblings - wanted to learn how to be a mechanic, but the family didn't know the school took in students with criminal records.He said his son was roommates with Arbelo, who the police report describes as the primary attacker in the group accused of killing Amaya Guardado. Police haven't disclosed any motive in the death.Amaya Guardado's parents said he was a quiet boy who kept to himself for the most part and never bothered anyone. The parents said they believe the suspects had been bullying the younger, bespectacled boy and taking money from him before his death."When you go there, they only show you the good," Santos Amaya said of the school, speaking in Spanish. "They don't show you the ugly."A telephone message left late Friday with the US Department of Labor wasn't immediately returned. In a statement released on Wednesday, a Labour Department spokesperson said security is their top priority.In the arrest report, police said Strickland complained about missing the start of the beating because she walked away to urinate in the woods.Sex after murderThe school is located in a remote area of Miami-Dade and is surrounded by wooded areas, with small roads leading into the woods but nowhere else.According to the report, Amaya Guardado was ordered to lie in the shallow grave after the initial attack, but he made one last attempt to fight off the assailants. That's when police say Arbelo struck Amaya Guardado several more times with the machete until his face caved in. The suspects then pushed Amaya Guardado into the grave and buried him, according to the report. Strickland and another suspect stayed behind after the killing to have sex, it added.The suspects cleaned up the scene, burned the victim's belongings and their own clothes and got rid of the weapon, authorities said.Strickland was charged on Wednesday, while Arbelo, Lucas and Colon were arrested last week. An attorney for Lucas said he couldn't comment on the case. An attorney listed for Colon and Strickland said he had withdrawn from the case, and it wasn't immediately clear if replacements had been assigned. An attorney listed for Arbelo didn't return calls or emails.Attempts by The Associated Press to reach family members of the suspects have been unsuccessful.