COLUMBIA -- A Bible-only policy for inmates at the Berkeley County jail is stricter than policies governing reading materials allowed some of the country's most dangerous inmates, a former warden who ran the tough federal penitentiary that replaced Alcatraz said in court documents.

John L. Clark, who served for years as warden of the U.S. Penitentiary in Marion, Ill., filed an affidavit that states that letting prisoners read various materials kept even that Supermax prison safe. That complex replaced Alcatraz when it closed in 1963.

"Allowing ... Marion's prisoners to access reading material was a component of effectively managing the facility's high security population," wrote Clark, a former assistant director of the federal Bureau of Prisons. "The policy of allowing prisoners to receive publications did not create any threats to good order or security."

He added in the affidavit, filed Monday in federal court, that educational materials, newspapers, books and magazines broaden prisoners' and detainees' ability "to function in and relate to mainstream society upon their release."

Clark's statements were filed by the Prison Legal News, a monthly legal journal by the Human Rights Defense Center that is at the center of a federal lawsuit in South Carolina. Since 2008, the journal's publishers have tried to send magazines, letters and self-help books about prison life to several inmates at the Hill-Finklea Detention Center, but copies were returned after jail officials said staples inside posed a security risk.

"Our inmates are only allowed to receive soft-back bibles in the mail directly from the publisher," First Sergeant K. Habersham wrote in a July email to publishers, explaining the jail's policy. "They are not allowed to have magazines, newspapers, or any other type of books."

The American Civil Liberties Union sued the jail in October on the publication's behalf, arguing that authorities at the jail in Moncks Corner, about 100 miles southeast of Columbia, are violating the magazine's and inmates' constitutional rights. Jail officials then told The Associated Press the jail didn't have a library and that the only reading material allowed is paperback Bibles.

Since then, an attorney for the jail has said inmates are allowed non-Christian religious texts -- including vampire and witchcraft texts -- as long as the books are soft-sided and meet other physical requirements, such as the absence of staples.

The ACLU, which has asked a federal judge to block the jail's rules while the lawsuit proceeds, also has argued that legal pads with staples in them are available for inmates to purchase at the jail's commissary.