There is no document giving General Cadwalader purported authorization to suspend the privilege of the writ until after CJ Taney issued his decision.
Regarding the issuance of the writ, by law CJ Taney could not simply deny the writ. Also by law, General Cadwalader was required to make a return. General Cadwalader could not retroactively invoke a suspension of the privilege of the writ.
Currently codified under 28 USC 2243, the applicable part reads, "A court, justice or judge entertaining an application for a writ of habeas corpus shall forthwith award the writ or issue an order directing the respondent to show cause why the writ should not be granted, unless it appears from the application that the applicant or person detained is not entitled thereto."
Additionally, "The writ, or order to show cause shall be directed to the person having custody of the person detained. It shall be returned within three days unless for good cause additional time, not exceeding twenty days, is allowed.
The person to whom the writ or order is directed shall make a return certifying the true cause of the detention."
The reason for suspension of the privilege of the writ was clearly to jail political prisoners, upon any pretext, and be able to keep them unlawfully imprisoned.
Page 591 THE MARYLAND ARRESTS.
The old police when disbanded consisted of 416 persons. Twenty-seven are in our service. Several have been discharged. There are now about 350 left. The great part of them are obscure and inoffensive persons. Some of them are Union men. There are I am confient not over forty or fifty who would not take the oath of allegiance. There are some very mischivous, worthless fellows, but they are quiet. We only want a pretext for arresting them.
-- Major-General John A. Dix
Page 592 PRISONERS OF WAR, ETC.
GENERAL: Fort McHenry which has not sufficient space for the convenient accommodation of the number of men necessary to man its guns is crowded with prisoners. Beside our own criminals awaiting trial or under sentence we have eleven State prisoners. To this number six more will be added to-morrow.
-- Major General John A. Dix
Page 594 PRISONERS OF WAR, ETC.
You will please send under a sufficient guard all the political prisoners and prisoners of war now at Fort McHenry except those indicted but including Marshal Kane by an inland route to New York, preferably by the Chesapeake and Delaware Canal.
-- E. D. TOWNSEND, Assistant Adjutant-General.
Thirty political prisoners left Fort McHenry this day for Forts Columbus and Lafayette via the dealware and Chesapeake Canal and Camden and Amboy Railroad under a guard of eighteen enlisted men -- Major-General John A. Dix
Page 595 THE MARYLAND ARRESTS.
The arrest of W. Wilkins Glenn,* the proprietor of the Exchange, has given intense satisfaction. Beale Richardson and his writing editor Joice, of the Republican, are very violent and would grace the Tortugas. If the exchange should go on a Doctor Palmer and a William H. Carpenter are the ostensible editors, and both write with bitterness. They too would do well at Tortugas.
-- W. G. SNETHEN.
Page 597 THE MARYLAND ARRESTS.
SIR: The general-in-chief directs that you send by the first suitable conveyance to Fort Lafayetten, N. Y., the political prisoners mentioned in your letter to the Secretary of War of the 15th instant.
-- E. D. TOWNSEND, Assistant Adjutant-General.
SIR: The general-in-chief directs me to say that orders have been sent to Major-General Wool to transfer from Fort Monroe by the first suitable conveyance Honorable Henry May, Messrs. Winans, Brown and twelve other political prisoners arrested in Baltimore to Fort Lafayette.
-- E. D. TOWNSEND, Assistant Adjutant-General.
You are confused. There is no documentation concerning the purported "arrest warrant" for Taney.
However, April 27, 1861, President Lincoln, as an emergency measure in the face of armed insurrection and the absence of Congress, lawfully suspended (the privilege of the) writ of habeas corpus by proclamation directed to Lt. General Scott. On May 16, Scott authorized Maj. Gen Cadwalader to arrest and detain individuals in certain circumstances.
"Regarding the issuance of the writ, by law CJ Taney could not simply deny the writ."
Not true. Taney could have recognized the circumstances of the war surrounding, admitted his personal relationship with Merryman, and either declared he had no jurisdiction or recused himself. Instead, he steered toward confrontation.
The purpose of the suspension is to allow the government to prosecute the war against the unlawful insurrection, without interference by disloyal judges hoping to spring their friends, neighbors, and fellow-travellers out of jail.