A witness on Thursday described in horrifying detail how accused drug kingpin Joaquin "El Chapo" Guzman brutally murdered people with his own hands.

In striking testimony during Guzman's trial, Isaias Valdez Ríos, who started in the drug lord's security circle in 2004 and later became one of his pilots, claimed his boss tortured his enemies. He said Guzman killed three members of other Mexican cartels who crossed his path -- by shooting them in the head, burying them alive and burning them to the bone.

As the witness was describing violent episodes carried out by El Chapo’s men, the prosecution asked him if he had ever seen the defendant directly involved in the killings -- and he started recalling two events.

Around 2006-07, he said, the reputed kingpin sent one of his secretaries to pick up some things from his partner "El Mayo" Zambada. Turns out it was an "arete," meaning a person from the Arellano Feliz cartel with whom El Chapo was at war. He had been kidnapped, beaten up and interrogated before and was brought on Mayo's plane. El Chapo’s men took him to a place where they used to sleep in the mountains of Sinaloa and next to the boss’ cabin.

They told Guzman this person “had been severely tortured” and that he had burns all over his body, with marks from “an iron” to the point that his T-shirt was stuck to his body. His feet and hands were tied and he was blindfolded. Guzman allegedly said, "'How could they send me this a--hole like that,'" Ríos recalled.

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In spite of that, it was not until two days later that Guzman decided to go see him and started interrogating the "arete," asking about what happened with members of the Arellano Feliz cartel, Ríos testified. He said they spoke for about 20 minutes before the man was moved to another location where he stayed “for days.” Afterward, Guzman's men said the person already had a "really bad odor" and was starting to "decompose."

According to Ríos, at the orders of the defendant, the "arete" was put on an elevated area in front of a small graveyard they had dug. He was still blindfolded with his hands and feet tied up and could only hear them. The reputed kingpin started interrogating him again and then just pulled out a “25-caliber” and “shot him.” “'Motherf---er', he said.”

Rios alleged that "the person was (still) gasping" and he was dumped and buried alive.

During this testimony, the defendant looked fidgety while staring at the witness, touching his chin and scratching his head at times. His wife, Emma Coronel, looked expressionless as she sat in the audience.

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Ríos recalled another occasion, in Mexico's El Dorado, Durango, when two members of the Zetas cartel -- also the defendant’s enemy -- were kidnapped at his orders. They were blindfolded and put in a shed, and his men started "beating them up" so they would start revealing information.

As Guzman arrived with others, he "requested a long branch" and “started torturing them." After the beating, "their bones were broken, they couldn't move,” Ríos said. “He (Chapo) said, ‘Motherf---ers, how could you be working with those people and betraying us?'"

It's a betrayal to be from one state in Mexico and work for a cartel from a different state, the witness explained.

This beating would last “around three hours” and he would order his men to dig a large hole to make a bonfire to throw them in but not until Guzman shot each of them on their heads with a rifle. Guzman didn’t want any bones left and when finished, they “ground them up."