NEW : Former Peruvian president sentenced to 25 years in prison . Charges against Alberto Fujimori stem from 1990s ' ` ` dirty war '' , already serving time on previous abuse of office conviction .
NEW : Former Peruvian president sentenced to 25 years in prison . Charges against Alberto Fujimori stem from 1990s ' `` dirty war '' Fujimori already serving time on previous abuse of power conviction .