John Merryman, a Maryland resident and avowed secessionist, was arrested and detained in Fort McHenry. Chief Justice Roger B. Taney, then sitting on the Circuit Court bench, found that Merryman was being held unlawfully and issued a writ of habeas corpus. The jail official refused to comply, citing the fact that he was acting in compliance with an Executive Order from President Lincoln.
Taney held that only Congress had the power to suspend habeas corpus, not the president. Indeed the Constitution (Article 1, Section 9) is silent on who can make the decision to suspend.