Thomas J. Scotto, the president of the N.Y.C. police detectives union has been named as an unindicted co-conspirator in what federal prosecutors say was an organized-crime scheme to use kickbacks to union leaders and mob threats and violence to tap pension funds, inflate stock values and defraud thousands of investors. Scotto, who has led the Detectives Endowment Ass'n since 1986, was named by prosecutors in papers filed in U.S. Dist. Court in Manhattan recently to supplement information in 16 indictments that brought charges against 120 people in Jun. 2000 in a wide conspiracy.