I know this is a long shot, but it's worth a go...
About 5 years ago, we used to have a channel called Current TV which no longer exists. I watched a documentary on there a couple of times about gangs/ violence in El Salvador. Google keeps taking me to a well known documentary called Gangs of El Salvador which is not the one I remember!
Things that have stuck in my head: the music at the end, Latin American hip hop played over scenes of a poverty stricken area in the evening, the lyrics subtitled; interviews with an older gang member in prison who had fallen foul of the gang and at one point is talking about how the gang has killed/ will kill his wife and will try to kill him.
If anyone else can remember this, especially the right title, I would be both amazed and delighted :)