It is Mexico’s answer to gangsta rap – but with a body count that makes the badlands of South Central Los Angeles look decidedly tame.

The songs are known as narcocorridos: folk tunes, set to frantic polka rhythms, many of which have lyrics that celebrate drug lords and human traffickers and how they stand up to the authorities. But the music – whose lyrics are often used as PR by gang leaders, sometimes citing real dates and places of crimes – is coming at an extraordinary cost, with at least eight performers killed in gruesome circumstances this year.

However, it is the most recent case that has shocked Mexico and prompted the deployment of the army to the north of the country.

The victim was Zayda Peña, 28, who was known for her antigang views. The husky-voiced singer played a musical genre known as grupero, a mixture of rock beats and folky accordion melodies. Singing with her band, Zayda y los Culpables (Zayda and the Guilty Ones), her songs chronicled the lives and love affairs of borderline vagrants, workers and criminals.

One of Peña’s songs was entitled Tiro de Gracia, a term for the final shot to the brain in a gangland killing. Her popularity was such that a montage of her videos even made it on to YouTube.

She was seriously injured in a shooting at a hotel on Friday, which left two others dead. She was taken to a hospital in Matamoros, across the border from Brownsville, Texas, where she underwent emergency surgery.

But it was what happened next that astonished even the Mexican authorities: while she was being treated, a gunman burst into the intensive care unit and killed her with two shots to the face. It was the tiro de gracia that she had once sung about. In response to the murder – and the killings two days earlier of six men, including a former mayor, in the nearby town of Rio Bravo – Felipe Calderón, the Mexican President, ordered hundreds of troops to the north, which is reportedly controlled by the so-called Gulf Cartel. Osiel Cárdenas, the cartel’s leader, was recently extradited to Houston.

Authorities say that the most troubling part of the recent spate of violence against musicians is that some of them are not even famous for singing narcocorridos. This was the case with Peña and with Sergio Gómez, the lead singer of K-Paz de la Sierra, and the recipient of a Billboard Latin Music Award last year.

His body was found on Monday near Morelia, the Michoacán state capital. He had been beaten, burnt in several places and choked. Magdalena Guzmán, a spokeswoman for the Mexican Attorney-General’s office, said that it was impossible to tell if it was the choking that had killed him.

“The blows were so severe that they, too, could have been fatal,” she said.

Local police have suggested that Peña’s shooting might have been a “crime of passion” – a common explanation for violence against women.

Mexicans are now asking themselves if the violence is being worsened by the narcocorridos, or if the narcocorridos are simply a byproduct of the increasing power of gangs. So far this year 2,500 Mexicans have died in gangland killings.

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