FARGO, N.D.—A Texas man says he will plead guilty in a wide-ranging investigation into the synthetic drug deaths of two teens in North Dakota and Minnesota.

John Polinski, of Houston, is charged in federal court with conspiracy to distribute controlled substances resulting in serious bodily injury and death. The charge carries a maximum sentence of life in prison.

Fifteen people have been charged in the investigation dubbed "Operation Stolen Youth," and all but Polinski have entered guilty pleas.

Authorities say the hallucinogens caused the June 2012 deaths of 18-year-old Christian Bjerk, of Grand Forks, and 17-year-old Elijah Stai, of Park Rapids, Minn.

Neil Fulton, who heads the public defender's office in the Dakotas, filed a change of plea notice Monday for Polinski. A plea hearing has not been set.