Colombian troops had killed hundreds of innocent civilians for no apparent reason other than to boost rebel body counts, U.N. investigators found. Typically, the victims were down-on-their-luck men lured to their deaths with job promises then dressed in military fatigues and registered as guerrillas slain in combat.

Five years after the scandal broke, roughly one-sixth of the soldiers accused have gone to trial or pleaded guilty, only a handful of the convicted holding the rank of major or higher. In all, authorities registered some 3,900 cases of alleged extrajudicial killings involving security force members.

Human rights activists say they are afraid a new law pushed through Congress by President Juan Manuel Santos in June will make it even harder to pursue those responsible, particularly senior officers. The law, which is under review by the Constitutional Court, would broaden the military justice system’s jurisdiction and narrow the definition of extrajudicial killings.

Santos says the reform is needed to assure armed forces members they have nothing to fear from making peace with the country’s main leftist rebel group, the Revolutionary Armed Forces of Colombia, or FARC.

But activists fear the reforms could hinder prosecutions of past and future war crimes by security force members and thus hurt prospects for peace talks launched in Cuba last year.