Colombia Reports said Cesar Perez was found guilty Wednesday and is awaiting sentencing. He is expected to receive 25 to 30 years in prison.
An ex-paramilitary leader, Negro Vladimir, accused the former congressman of financing the massacre in Segovia to gain political control of the area, Colombia Reports said.
The massacre came after the leftist Union Patriotica party won elections in Segovia in 1988.
"He [Perez] asked Henry de Jesus Perez and Fidel Castano to remove the leftists from Segovia, a municipality where the majority supported the Union Patriotica, so he could have absolute political control over the region," Vladimir said.
The massacre was not investigated until 2010, Colombia Reports said, and officials captured Perez in July of the same year.