On a Saturday afternoon in December, three Honduran boys walked out through the gates of the blue stucco YMCA shelter for unaccompanied child migrants in Tijuana, and turned past the gas station next door on to Cuauhtémoc Boulevard for a walk.

Their destination was a sports centre-turned-migrant camp to visit people they’d met travelling north with a caravan of other Central Americans.

Two of them never returned: the bodies of Jasson Ricardo Acuña Polanco and Jorge Alexander Ruiz Duban, 16 and 17, were found the following morning; three people were arrested for their murder.

The boys were tricked, abducted, tortured and killed; the survivor escaped with wounds to his throat from attempted strangulation and remains acutely traumatised.

The horrific murder brings into brutal focus the vulnerability of migrants forced to “remain in Mexico” under the new US policy for asylum seekers.

On a recent visit to Tijuana, Unicef’s deputy representative in Mexico, Pressia Arifin Cabo said that migrant children must be protected from danger – on both sides of the border. “Migration is not a crime, and many of these adolescents are travelling alone, unsure of what to do,” she said.

Boys at the Casa YMCA, a shelter for unaccompanied child migrants in Tijuana. Photograph: Ed Vulliamy

The Guardian has traced the Honduran boys’ final days, on the basis of the surviving child’s account – we’ll call him Lázaro – as told to staff at the shelter and the Tijuana district attorney, José Alberto Álavarez.

“They had been with us two or three weeks”, said Uriel González, who runs four YMCA shelters for unaccompanied child migrants along the border. “They left the casa by themselves, and one of two women started talking to them”.

According to González, the woman lured them to a white-gated house near the city centre with the promise of sex and money. Eventually, “she took them to a house and they were not allowed to leave. That’s when they realised they’d been kidnapped”.

According to Álvarez, the initial motive appears to have been theft, but when it became clear the boys didn’t have any cash the kidnappers decided to extort money from their relatives captives – and then started to torture them.

The Hondurans were tied to chairs undressed and tortured with scissors.

Two of the boys were murdered – one choked on a stick, the other strangled – but somehow Lázaro escaped and found his way back to the shelter, González said.

The bodies of Acuña and Ruiz were dumped the same night near a school nearby.

A woman who lives nearby recalled: “There was a commotion. People said: there are bodies over the road! I saw them covered with a blanket. The police arrived, lights and noise, and took them away”.

Officers later took a statement from Lázaro and then asked him to recreate the route of his abduction, said Álvarez. “And, unbelievably, there was the same girl, walking the same street, doing the same thing – two days later. She told us where the house was, and there we found one man who took us to the other guy.”

The woman and two men were arrested and charged with abduction and murder.

Because the victims were from the migrant caravan, the killings have drawn rare attention in Tijuana – where such deaths usually fail to turn a head.

Local human rights activists have linked the double murder to a growing hostility towards Central Americans that has grown in Tijuana since the migrant caravans first arrived last year.

“It’s hard not to think that a climate of xenophobia promoted by the state’s own institutions is not a breeding ground for this type of action”, said the president of the Baja California State Commission for Human Rights, Melba Adriana Olvera Rodríguez, citing what she called inflammatory language by municipal leaders.

The house where the boys were tortured and murdered. Photograph: Ed Vulliamy

Prosecutor Álvarez insists the deaths reflect the spiraling violence which has afflicted Tijuana: 2,502 were killed in the city last year – a rate of 126 per 100,000 inhabitants.

“These were small-time drug dealers working the street, themselves intoxicated. These terrible murders illustrate the social decomposition we see in Tijuana,” he said.

Both men arrested have records of drug dealing, and admitted low-level connections with cartels.

“At the root of this are drugs”, says Álvarez, “but most of the murders now are by petty drug-dealers; people fighting for turf for the domestic market in methamphetamine.

“[This case] has attracted attention because the victims were from the caravan. If they had not been, no one would know about this – they would probably be just two more murder victims in Tijuana.”

Weeks after the murders, the YMCA shelter is still in shock; most of the youngsters here remember the victims well.

“They were the same as us, who came here hungry and thirsty,” says one boy, José. “We came for lack of work and because gangs back home threaten you with death to get money even if it’s just a few pennies .”

González fears for the safety of the surviving boy. “The kidnappers threatened to kill him if he spoke. He just wants to get the hell out of Mexico, but cannot until they have closed the case,” he said.

Local authorities say Lázaro will have to testify, but after that there is no guarantee the boy will be granted asylum in the US.

The corner on Calle Quintana Roo where the bodies were dumped, two-and-a-half blocks away. Photograph: Ed Vulliamy

There is s a cruel final twist to the tragedy.

On Monday 17 December, two Californian congress members, Nanette Barragán and Jimmy Gómez, came to Tijuana, to join a protest against US authorities’ refusal to allow asylum seekers to make their claim, as is their right under US and international law.

After waiting all night at the crossing, they finally accompanied 20 migrants through, including 8 minors. There were supposed to have been nine – also on the list was Lázaro.

“He should be in the United States now, processing his asylum claim” said González. “Instead he is here, traumatised, waiting for his chance to come, living this nightmare”.

