He was best known for the national attention drawn to some of his rulings in famous cases, several of which were upheld by the United States Supreme Court.

[1][3] Judge Cook, in the case of Cordelia Botkin, made the first decision for a crime committed in two different states, Delaware and California.

He also sentenced to death the medical student, Theodore Durrant, who was convicted in November 1895, for the murder of two young women nine days apart in a church.

[7][8] As an attorney, Cook defended John McNulty, on his appeal of his death penalty sentence, for whom the gallows was erected eight separate times.

Cook stayed the execution and, taking the case to the U.S. Supreme Court, had the sentence reduced to six years in prison.