US troops have piled concertina wire along the US-Mexico border, which has been criticized as security theater with little practical use.

In Tijuana, where violence is climbing, Mexicans have repurposed the wire for their own protection.

Voluminous bundles of concertina wire strung up by US troops around ports of entry on the US-Mexico border have been criticized as displays of security theater that serve no real purpose.

But residents in Tijuana, which recently topped a list of the most violent cities, appear to be repurposing the wire for their own security amid a protracted increase in crime in the city.

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The razor wire was installed in the fall along the border wall between Tijuana and San Diego by US troops and contractors. It was meant to deter migrants who have arrived in the city as part of large caravans in recent months.

But some of that wire has gone missing and has reappeared on homes in Tijuana, raising suspicions that residents either took it and reinstalled it themselves, or thieves stole it and sold it to people in the Mexican city.

A US Customs and Border Protection agent. Reuters

The wire is easy to spot on the homes because it's the same size as the coils of wire that were put on the wall and because such wire is not sold in Mexican hardware stores, according to Milenio.

Mexican officials were aware that wire installed on the border wall was no longer there, Marco Antonio Sotomayor Amezcua, the municipal security secretary in Tijuana, said.

"We know about the theft of the concertina from the US authorities who have asked us for help" through intermediaries, Sotomayor said, adding that Mexican authorities have responded, but by the time they reach areas where potential theft is reported, the perpetrators are gone.

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Mexican police have arrested 15 to 20 people in the past week in relation to the theft, according to Reynaldo Gonzalez Mora, the director of Tijuana's border-liaison unit. Gonzalez said those apprehended were mostly Mexican citizens or people who have been deported from the US.

They are "people who have problems with drug addiction and live mostly on the street," he said, according to The San Diego Union-Tribune.

The reports of theft come days after Tijuana was named the most violent city in 2018, with a homicide rate of 138.26 per 100,000 people, according to the Citizens' Council for Public Security, a Mexican civil-society group. By comparison, San Diego's homicide rate was just more than 2 per 100,000 people.

Forensic officers and policemen work in the area where 15 men were killed in a gun battle in Tijuana, Mexico, on April 26, 2008. REUTERS/Stringer

The list of 50 cities included 42 cities in Latin America, with 15 of them in Mexico. (San Juan, Puerto Rico, and four other US cities were on the list.)

Tijuana was also on the list for 2017, when it was in fifth place with 100.77 homicides per 100,000 people. (The Mexican cities Acapulco and Los Cabos were ahead of it in 2017; in 2018, Acapulco was second, and Los Cabos had moved off the list.)

But the city has seen a sustained increase in deadly violence. In the past, crime in Tijuana has largely been driven by competition between organized-crime groups vying for control of lucrative smuggling routes across the border.

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Large criminal groups are still fighting for influence in Tijuana; it's believed the Sinaloa cartel is clashing there with the Jalisco New Generation cartel and its local partners, operating under the name Tijuana New Generation cartel.

But the recent bloodshed in the border city appears to be driven by fighting over low-level drug sales, mainly of methamphetamine, with local dealers and others killing and dying for control of street corners.

According to data released by the Mexican state of Baja California, there were 2,519 homicides in Tijuana in 2018, a 41% increase over the 1,781 homicides during 2017. There were 365 homicides there in January and February this year, just short of the 368 killings over the same period last year.