Mara membership across Central America is put at 25,000
"The majority here have killed people. It's basically a requirement to be in the gangs."
Julio Cesar, now in his thirties, relaxes back in his chair, revealing a slight paunch bulging underneath his t-shirt.
He was once a lithe and dangerous youngster who helped to found one of the most notorious gangs in Central America - the "Mara Salvatruchas".
It began in Los Angeles in 1980.
Hundreds of thousands of Salvadoreans had fled to America to escape the brutal civil war back home.
Their displaced children banded together.
Sitting nearby is his old friend, Ernesto Miranda, who opens his shirt to reveal the initials of the gang, "MS" emblazoned across his chest.
Tattoos are the trademarks of the Maras.
Ernesto co-founded his gang at only 11 years of age
"We had to start the group to defend ourselves," Ernesto says.
"In the beginning there were 30 of us. We were around 11 years old."
Watching them quietly is Carlos Alberto Vasquez.
He wears a striped shirt and designer glasses. He looks like he could be a city lawyer, until you notice the greenish tattoo creeping up from under his collar.
Carlos was thrown out of the US for kicking a member of a rival gang to death.
When the peace accords were signed in El Salvador in 1992, America deported most of its unwanted immigrants.
They returned to their country and brought their gangs back with them.
Leaving the gangs
The group which Ernesto, Julio, Carlos and their friends spawned in LA now has an estimated 25,000 members across Central America.
But its founders have rejected their own creation.
Now, they are working with an organisation which helps youngsters to leave the gangs.
They sit in a circle with around 20 other young men on a peaceful, terracotta-tiled terrace overlooking green fields.
This is very different from what most here are used to - coming from the slums of San Salvador, where shacks made out of corrugated iron line dusty pathways.
"We opened the door to the devil and he came right in," says the spiritual leader of the San Andres Foundation, who urges the young men to let Jesus replace the violence in their hearts.
Accompanied by a woman on a guitar, there is a group prayer.
One teenager, wearing a white T-shirt and heavy necklace, his closely-shaved hair wet with gel, looks unconvinced but joins in anyway.
Finding it hard
For others, being part of this group has clearly changed their lives.
A 25-year-old former tattoo artist, Jaime Ernesto Ranchos, shows the "MS" of the Mara Salvatrucha scrawled across his back.
Jaime is rebuilding his life after leaving his gang
Two years ago he was heavily addicted to crack cocaine and robbed shops and banks for a living.
"The worst thing was that my six-month old son was malnourished because my girlfriend couldn't afford to buy him any milk," he says.
"He'd just get the occasional fizzy drink, because I was using all the money for drugs.
"Now, she won't let me see him any more."
But, with the help of this foundation, Jaime now has a job and is out of the gang.
But he finds it hard.
"It's like losing a family," he says. "The friendship is the most difficult thing to leave."
Combating the 'assassins'
The Maras are believed to be largely responsible for an epidemic of street violence plaguing Central America.
Resolving the problem will be one of the toughest jobs for El Salvador's next president.
The favourite to win elections on Sunday is Tony Saca, who favours continuing the tough approach started by the current government.
A temporary law passed last year allows anyone displaying a gang tattoo to be arrested.
"We must remember who we are talking about - we are talking about assassins," Mr Saca says.