An Alabama 13-year-old found dead in a wooded area last month was beheaded after she saw two men stab her grandmother to death, an investigator testified Thursday. The grisly details of Mariah Lopez’s slaying came out during the preliminary hearing of Yoni Martinez Aguilar, AL.com reported. Aguilar, 26, and Israel Gonzalez Palomino, 34, are each charged with two counts of capital murder in the deaths of Lopez and her 49-year-old grandmother and legal guardian, Oralia Mendoza. Palomino is also charged with possession of methamphetamine. Members of the middle schooler’s family wept as Investigator Stacy Rutherford testified about the details Aguilar, who was Mendoza’s live-in boyfriend, gave in a statement following his June 14 arrest. Related story: Police: 13-year-old girl dead in ‘brutal’ killing, grandmother’s body also found According to AL.com, Aguilar told detectives that Mendoza was involved with the Sinaloa cartel, considered to be the world’s most powerful drug trafficking organization. Rutherford testified that the defendant told investigators that he, Palomino, Mendoza and a woman named Leticia Garcia traveled June 2 to Norcross, Georgia, where they picked up a quarter kilo of meth for the cartel. Along the way, something went wrong and Palomino became suspicious that Mendoza and Garcia, who was also tied to the cartel, might be setting him up, Aguilar said in his statement. WAAY in Huntsville reported that Rutherford testified that sometime after the group returned to Huntsville, Palomino learned that Mendoza had removed the SIM card from her cellphone. He also found a text she sent during the drug run to Georgia, in which she asked an unknown woman to pick up her granddaughter, who was with Palomino’s wife, because she feared that she and her granddaughter were in danger. Early on June 4, the men woke Mendoza at their Huntsville home and told her that they were taking her and Lopez, who had special needs, somewhere safe, AL.com reported. Rutherford testified that they were instead taken to Moon Cemetery, located about 15 miles southeast of the city in Owens Cross Roads. Palomino and Mendoza argued in the cemetery about the drug deal and Palomino stabbed the grandmother multiple times, leaving her for dead, Aguilar told investigators. Lopez, who witnessed her grandmother’s slaying, was taken to a wooded area about 2½ miles from the cemetery, where Aguilar said Palomino forced him to kill the girl. Rutherford testified that Aguilar told investigators he was holding the knife when Palomino grabbed his arm and moved it back and forth in a “sawing motion,” with which the girl was beheaded. Aguilar said he participated in the slayings out of fear. “He said he was fearful of Israel,” Rutherford testified, according to AL.com. >> Read more trending news The men left the teen’s body where she was killed and stopped to clean Palomino’s car, the detective said. Mendoza was reported missing two days later by worried relatives, WAFF in Huntsville reported last month. Lopez’s body was found the following day. Madison County investigators released information describing the items the body was clothed in: red pajama pants with gingerbread men on them, as well as a pink undershirt and black tank top. The news release also indicated that the young victim had a cerebral shunt. Lopez’s mother -- who is also Mendoza’s daughter -- showed up at the Madison County Sheriff’s Office a short time after the description was released and told investigators that the body might be that of her daughter, Sheriff’s Office officials said. Dental records provided a positive identification a week later. Mendoza’s body was found at the cemetery June 15, after Aguilar gave his statement to investigators. She was also identified through dental records, Sheriff’s Office officials announced June 27. Aside from Aguilar’s alleged confession, investigators have collected physical evidence they say links the men to the slayings -- including the suspected murder weapons. AL.com reported that Rutherford testified one knife was found under Palomino’s mattress and the other was found under Aguilar’s mattress. Despite the men’s cleanup efforts, blood was also found in Palomino’s car, the investigator said. Both men’s cellphones also “pinged” in the area of the killings during that time frame, the news site said. The slayings shocked the community, particularly those at Challenger Middle School, where Lopez was a student. The school’s Parent-Teacher Association last month set up a memorial account to help her family pay for her and her grandmother’s funerals. “No one is prepared to lose a child or other relative at such young ages,” a statement from the PTA said. “With the untimely passing of two family members, one can imagine the mounting costs of funeral and burial expenses that the family faces in addition to the unparalleled grief that is felt as well.” The “Mariah Lopez and Oralia Mendoza Memorial Account” was established at Wells Fargo, with donations set to go directly to the funeral home. “Anything in excess of those costs will be given to the immediate family to assist with other expenses and needs,” the PTA statement said. Lt. Donny Shaw, a Sheriff’s Office spokesman, last month credited the community with helping to quickly bring the search for Lopez’s and Mendoza’s killers to an end. “For a murder where there were no indications, no witnesses, nothing to lean on when we began with it, the Hispanic community, the partners, the media, we’ve been able to do a phenomenal thing in just a little over seven days by coming to the arrests of two individuals,” Shaw told WAFF. Both Aguilar and Palomino are being held without bail in the Madison County Jail. Palomino is also being detained on a hold for U.S. Immigration and Customs Enforcement. His preliminary hearing in the case is scheduled for Monday.