Another contractor has been charged as an Army Corps of Engineers employee is expected to plead guilty in one of the largest federal contracting bribery schemes in United States history, charging documents said. Robert L. McKinney, founder and president of the Waldorf-based Alpha Technology Group, was charged in federal court Monday with bribery of a public official, documents show.

He joins four other defendants — two Army Corps contracting officials and two businessmen — charged in the alleged $20 million kickback scheme.