MEDELLÍN, Colombia -- The last time Sandra Asprilla saw her son Esleyder alive, the 11-year-old was on his way to play soccer.

The next day, his body was found alongside that of his best friend Esteban, also 11.The pair had been tortured, murdered and left in a sack in a makeshift grave.

In Comuna 13, a violence-prone district of Medellín, death is only too common, but it usually involves teenagers and young men caught up in a war between neighborhood gangs battling for control of the city’s underworld. In this district of 135,000 people, 161 were murdered in 2012 and 22 are missing.

“The deaths, the themes of the war here, are over ‘invisible borders,’ or gossip, or because people are linked [to gangs], or suspicion, or because they are forced into the war and refuse to fight,” said Fernando Quijano, director of Corpades, a Medellín human rights group.

But the brutality of the boys’ murders — they were hacked with a machete — and their age has many in this community outraged.

The story began on Feb. 16 when the boys hitched a ride on the back of a supermarket delivery truck from their neighborhood of Nuevos Conquistadores to El Corazon, where they were playing with a younger friend when three armed men arrived and sent the younger boy to give notice that the two had been taken away.

The neighborhoods sit on either side of a war between the ‘Oficina of Envigado’ crime syndicate, in control of the city’s underworld since the 1993 death of Pablo Escobar, and the Urabeños narco-trafficking organization, which is aggressively expanding on rival networks across the country.

The Urabeños’ area of influence surrounds Medellín, a keystone in the drug route between eastern production regions and coastal export points, and the organization offers weapons and cash to buy the loyalty of gangs in strategic districts in order to wrest control of the drug flow through the city.

In crossing the invisible border between gangs aligned to each group, the boys apparently became a target after being recognized by a criminal who had switched sides.

Asprilla said her son often went to the adjacent neighborhood to play.

Early reports indicated men loyal to the Urabeños carried out the murder. But Quijano said it is believed a man known as “Garillo” oversaw the atrocity.

Formerly operating in Nuevos Conquistadores under the Urabeños, Garillo now works for an Oficina-supported gang in a rural sector bordering Comuna 13 called Aguas Frias, where the bodies were discovered, said Quijano.

Quijano speculates they were tortured for information about how the gang is operating in Garillo’s old stomping ground.

But intimidation most likely is also a motive.

“The groups carry out these acts to generate fear within the population and maintain control,” says Carlos Arcila, coordinator of rights group Mesa de Derechos Humanos [Human Rights Table].

“Every 15 or 20 days, bodies turn up after acts like these. But because it isn’t children, it’s less publicized,” he said.

Later, eight people aged between 12 and 32 were detained in connection with the boys’ deaths. Among them was Garillo, aged 16.

When the boys’ funeral was held, some 300 people attended in an immense outpouring of grief. Some displayed placards indicating their outrage at such violence against children.