The website InSight Crime describes the US push for these actions in El Salvador and other Central American countries:
The US Federal Bureau of Investigation (FBI) will help train Salvadoran officials, including police and magistrates, in wiretapping operations, stated El Salvador's Attorney General Romeo Barahona. The funds provided by the US will come through the Central America Regional Security Initiative (CARSI).
The US has been pushing "intelligence-led policing" in Central America over recent years, advocating wiretapping operations across the region, according to a February 2012 US Congress report. With the passing of a wiretapping law in Honduras late last year, all seven Central American countries now have legislation in place that allows the practice.
The US had been pushing especially hard for such a law to be passed in El Salvador, it seems, with a leaked diplomatic cable revealing that "intense engagement" by US officials over a two-year period helped break a legislative deadlock over the new law. As well as being admissible in El Salvador's courts, evidence gathered from CIT operations can also be used in the US thanks to a Memorandum of Understanding (MOU) signed between the two countries in January 2011.