Three members of the feared Mara 18 gang imprisoned at El Salvador's Quezaltepeque prison formed the musical group following a truce in March with their arch-enemies, the Mara Salvatrucha (MS-13) gang.
The truce, brokered by Bishop Fabio Colindres, El Salvador's military chaplain, and Raul Mijango, a lawmaker and former guerrilla commander, has been surprisingly successful: the number of homicides in El Salvador plunged from 15 a day to about five a day virtually overnight, police figures show.
El Salvador, population six million, has a level of violence only second to Honduras -- the world's deadliest country -- in the region, with a homicide rate of 65 per 100,000 inhabitants.
Central America is a key transportation hub for illegal drugs, especially cocaine from South America, heading through Mexico to be smuggled into the United States. Mexican cartels like the violent Zetas have entered in the region and formed alliances with the local gangs.
Salvadoran officials have said that the gangs are responsible for 90 per cent of homicides in the country, and most of those killed are gang members.
Yet there are signs of a more peaceful future: on May 2 the two Salvadoran gangs agreed to stop forcibly recruiting youths, and declared schools "peace zones." The gangs had been targeting schools to recruit children as young as 12.
"We formed this group to cheer this peace process along with our songs," said Mario Hernandez, 20. He formed "Gangster Fury" along with fellow prisoners and gang members Jose Menjivar, 25, and Oscar Montano, 22.
The trio recently performed for some 200 jailed gangsters crammed into a 40 square meter (430 square foot) hall in sweltering heat.
"Gangster Fury" performed songs they wrote such as "Reflection," "Poor Street Children," and "My Mother."
The interns sweating in white t-shirts, followed the beat and clapped enthusiastically, identifying with the rapper's calls for national unity, hard work, and appeals to God's love to help face their problems.
According to the Security Ministry, there are 10000 gang members in six of the country's 19 prisons, and some 50000 gang members at large. El Salvador's prisons were built to hold 9000 inmates, but currently houses 24000.
The Quezaltepeque prison, located north of San Salvador and designed for 200 prisoners, currently houses 896 inmates as well as 19 children belonging to the female prisoners.
"We are prepared to make sure this peace process does not last only 10 or 15 years, we want to give it all for our people, for our families," said M-18 leader Ludwin Rivera.
"We don't want people to doubt our commitment and then raise obstacles," he said.
Patricia Mancilla, who represents the jailed female prisoners, urged Vanda Pignato -- the wife of President Mauricio Funes -- to help set up programs that will let them to rejoin society.
"We are asking her for a bit of attention, and that she come ... to see what we can give to the people. We are going to show that we can change, that we want to reenter society," Mancilla said.
William Galindo, a former gang member who became an Evangelical Christian pastor while in prison, called on the country's churches to "support" the gang members as they search "the path to God."