Two teenage boys were caught carrying a suitcase with a child’s head after a cartel kidnapped and decapitated him.
The children were apprehended by police in Mexico City’s Guerrero neighbourhood after dropping it.
Jose Rodrigo and Darwin, both 15, have since been placed into custody.
The victim has been identified as 14-year-old Alessandro N, who was kidnapped by four armed men on motorbikes after he left a football pitch on November 11, Mexican newspaper El Universal reports.
The Union de Tepito, a cartel based in Mexico’s capital, is believed to be responsible for the killing.
Alessandro’s family were asked to provide 800,000 Mexican pesos (£29,605) for his safe return.
However, negotiations were unsuccessful as the family were unable to come up with the money.
Local journalist Carlos Jimenez claims the men had already killed the 14-year-old before asking for the ransom.
The two detained 15-year-olds say they were promised money if they transported the body to a rubbish dump.
Less than two weeks ago, Alan Yair Silvestre Becerril, 12, and Hector Efrain Tolentino de Jesus, 14, were found dismembered inside a box being wheeled around on a sack barrow in Mexico City.
Both incidents are reported to have occurred in the capital’s historical centre in the Cuauhtemoc borough.
The Union de Tepito is also thought to be behind the murders of Alan and Hector, and two of its suspected members have been detained.
One is thought to have participated in the killing and torture of the children.
Police are also searching for connections with the second, who has so far only been charged with drug-trafficking.
Last October, members of the cartel created an altar to Santa Muerte using human skulls and other body parts .
Cops uncovered the horrifying site during a raid on five houses in the colonies of Peralvillo and Tepito in the municipality of Cuauhtemoc, Mexico City.
The 31 suspects, 26 men and five women, were all suspected of belonging to the La Union Tepito cartel.
The altar was reportedly made up of satanic masks and contained human remains along with skulls covered with blood.
Resident Martha N. claimed they carried out satanic rituals every three days to become “immune” to bullets.