An Illinois man who worked as a spokesman for a leading “darknet” marketplace that users accessed anonymously to buy and sell illicit goods pleaded guilty Thursday to a federal conspiracy charge in Atlanta.

Ronald L. Wheeler III of Streamwood, Illinois, worked for about two years as a public relations specialist for AlphaBay, which authorities have said was the world’s leading darknet marketplace until it was taken down through an international law enforcement effort in July. People used it to trade in illegal drugs, guns, counterfeit goods and hacking tools, among other things.