The former boss of a feared Colombian paramilitary group arrived back in the country on Tuesday after serving a 16-year jail term in the United States, and will participate in the country's ongoing peace process with armed groups, migration authorities said.Last year, leftist President Gustavo Petro asked that he be extradited after finishing his sentence so that he could serve as a "peace manager" in the government's negotiations with various armed groups in the South American nation.