A 13-year-old girl in Alabama was beheaded because she saw her Sinaloa Cartel-associated grandmother stabbed to death by drug traffickers, authorities have said.

Mariah Lopez and her grandmother Oralia Mendoza, 49, were killed on June 4 in Moon Cemetery outside of Huntsville, Alabama, prosecutors revealed in court on Thursday.

The horrifying new details in the case came to light in a hearing for 26-year-old Yoni Aguilar, who along with 34-year-old Israel Palomino is charged with two counts of capital murder in their slayings.

At the hearing, investigators testified that the grandmother Mendoza had ties to the Sinaloa Cartel, AL.com reported.

Mariah Lopez, 13, and her grandmother Oralia Mendoza, 49, (together above) were killed on June 4 in Moon Cemetery outside of Huntsville, Alabama

Yoni Aguilar (left) and Israel Palomino (right) are charged with two counts each of capital murder in the slayings

On June 2, two days before the murders, the two alleged killers joined Mendoza and another woman on a trip to Norcross, Georgia to score methamphetamine.

The two women were both linked to the notorious Sinaloa Cartel, investigators said.

Based in Mexico, the cartel was long run by Joaquín 'El Chapo' Guzmán, who is now in custody in the US pending trial.

The grandmother had previously dated Palominio and was living with and dating Aguilar at the time of her death.

The two men became suspicious of a double-cross when Palomino discovered that the grandma had removed a SIM card from her cell phone, and had sent texts to a mystery number during the drug run to Georgia, cops said.

Yoni Aguilar appeared in Madison County District Court on July 12, 2018 for a preliminary hearing in the killings

Mendoza (above) was Mariah's main guardian. Investigators say she was also a drug runner associated with the Sinaloa Cartel

Palominio and Aguilar woke the grandmother and her granddaughter in the middle of the night, warning them that they were in danger and saying they would take them to a safe place, according to testimony.

Investigators say the men then drove the victims to a cemetery and Mendoza was fatally stabbed in front of her granddaughter Mariah.

Mendoza was Mariah's main guardian. Mariah was on the autism spectrum.

According to police, Aguilar told investigators that Palomino then forced him to kill the girl by beheading her in a secluded area because she was a witness.

Police say they found two knives tied to the murders: one under Palomino's mattress, and the other under Aguilar's.

It's unclear whether Palomino or Aguilar has an attorney.