Thomas E. Mellon Jr., founder of Doylestown, Pa.-based Mellon & Webster, died Tuesday after eight years of treatment for pancreatic cancer.

After clerking for Judge William H. Hastie of the U.S. Court of Appeals for the Third Circuit, Mellon spent seven years in the U.S. Attorney’s Office, where he served as chief of both the narcotics unit and the criminal division. Mellon prosecuted the first endangered species case, which laid the foundation for today’s environmental law enforcement, according to a release from Reed and Steinbach Funeral Home.