A teenage girl has reportedly confessed to killing her 13-year-old pal in a WhatsApp message after the victim was found dumped in a river with concrete blocks.

Investigators say she had first been cruelly beaten and tortured before being shot with weights tied to her legs to keep her body underwater.

The death of Mari Luna Giraldo has shocked the residents of the town of La Victoria, in the Colombian department of Valle del Cauca, after she was reported as missing on 22nd March.

According to reports, she went to visit her 17-year-old friend in the town of Ansermanuevo and then disappeared.

Her body was found four days later on the banks of the Cauca River.

The local authorities have confirmed that her friend, whom she went to meet on the day of her disappearance, had confessed to taking part in her murder in a WhatsApp chat, where she also named three other people involved.

Nelson Dabey, head of the Valle del Cauca Police Department, said the victim’s body had “wounds caused by a firearm”.

In addition, the girl’s killers reportedly used two cement weights tied to the victim’s legs to prevent her body from floating to the surface.

The victim’s mother, Marisol Arango, has demanded justice for her daughter, adding: “I need the authorities to cooperate with me because they have not given me an answer about what they did to my girl.

“It is known that the police found her with weights tied to her little feet. They brutally tortured my daughter.”

As well as gunshot wounds, the victim was also found with head injuries and blows to her face, according to La Victoria mayor Mario Reyes.

The investigation is ongoing.