Newly published documents by the National Security Archive reveal why a grand jury refused to prosecute a Chicago Tribune reporter during World War II for a leak.

Correspondent Stanley Johnston was accused of revealing the United States cracked a Japanese code, which alerted the military to Japanese war plans before the Battle of Midway. A Tribune editor attributed the source of information to “naval intelligence.”

A prosecution was contemplated under the Espionage Act, but the government backed off because they feared what may happen if a trial publicized that the U.S. compromised the Japanese code.

The Justice Department under President Barack Obama fought against a lawsuit filed by the Reporters Committee for Freedom of the Press. It lost when a district court ruled in 2015 that disclosure would “result in a more complete public record of this historic event” and affirm the government is “open, in all respects, to scrutiny by the people.”

Yet, the government appealed, and it was not until September 2016, when the appeals court ruled against the government’s claim that a federal court had no jurisdiction to order the release of transcripts, that an effort to keep 75 year-old documents secret came to an end.

During World War II, the U.S. military expected journalists accredited as war correspondents to submit stories prior to publication for censorship—or what the Pentagon may now refer to as “prepublication review.” Johnston was accredited by the Navy at Pearl Harbor.

In grand jury testimony from August 18, 1942, Johnston indicated that he knew he was to submit for the purpose of censorship “all written or photographic material, either private correspondence, or anything for publication, released with the Navy or after my return.” Letters or dispatches were even to be subjected to censorship like any person in the military forces.

Johnston, who was Australian but recently obtained U.S. citizenship, also testified, “I have a son twenty years of age. The last word I had from my mother was that he had gone with the Australian Army to the war front. He is probably somewhere up there now where they are fighting.”

“If you think that I would do anything that would hurt the men in the United States Navy, or my son, there is nothing that I can do about it,” Johnston added. “If I am indicted in this case here, I know I haven’t done anything—there has been no intent, and they tell me there has to be intent. And if there is anything I have done, and I am indicted on this, it will wreck me forever. I know that in court it will be found out, it must; but that doesn’t help me. Meanwhile, my son will hear it, everybody else will hear it.”

Johnston, for his part, insisted in his testimony that he was not involved in the decision to attribute information about Japanese warships to “naval intelligence.”

To President Franklin Delano Roosevelt and the Navy, the  leak clearly correlated with a top secret dispatch from U.S. Pacific Fleet commander Admiral Chester W. Nimitz, which was sent on May 31 and contained details on Japanese warships involved in the Battle of Midway.

Navy Commander Morton Seligman was asked by the grand jury if he saw the Nimitz transmission. He denied knowledge of the transmission until the grand jury was able to show him he initialed a copy of the transmission that his ship received. Seligman later admitted it was possible he wrote down a list of ships on a piece of paper that Johnston could have found.

“Under ordinary conditions, I would say that if I personally left a paraphrase of a message that contained important information lying about, I would be very careless,” Seligman stated. “However, if I merely left a list of ships accidentally on my desk, a list of ships doesn’t mean anything, anybody can make a list of ships. Unless you know that the list came from the message like this, it doesn’t mean anything.”

Seligman did not think there was any threat of a leak because other than Johnston there were no civilians aboard. “These officers trusted each other, that is, they wouldn’t think a brother officer would grab a message like that, take it away secretly, and publish it, or anything.”

The grand jury was building a case against Johnston and possibly even managing editor J. Loy Maloney, but when Admiral Ernest King refused to allow testimony from any naval intelligence officers, according to John Prados, all the jurors had was the charge that “someone had utilized secret information.” Plus, it increasingly seemed the Navy may have mishandled information and failed to prevent Johnston from obtaining the sensitive information.

Prosecutor William D. Mitchell wrote in a memo on July 15 about “serious doubts” about the “prospects of conviction” as a result of “defects” in the Espionage Act.

In Mitchell’s opinion, the Navy censorship requirements did not forbid Johnston from giving stories to his editor before they were submitted to the Navy for review. The list of ships Johnston was alleged to have come across did not have markings indicating the information was from “secret dispatch.” It was left lying around, suggesting there was “nothing secret about it.”

Maloney could successfully argue he did not know the information was obtained from any writing or document and so he was not guilty of “willfully” offending the statute. And the Tribune Corporation could not be prosecuted if Johnston or Maloney were not guilty.

Mitchell regretted the fact that there was no possible path to prosecution. He was upset that Maloney and the Tribune had wanted to publish a “scoop” so badly they did not have the story censored first.

“I have reached this conclusion with regret because of the clear demonstration from the record in this case that Maloney’s eagerness for ‘scoops’ and ‘hot’ stories is such that if he thinks he can ‘get away with’ it, he will publish any material relating to national defense, in reckless disregard of any other consideration,” Mitchell contended.

Prosecutors in the Justice Department had no concerns about the impact on freedom of the press that may come as a result of pursuing prosecutions. In fact, they wanted to amend the Espionage Act to enable future prosecutions of journalists who engaged in similar acts.

Also, in a prior memo on July 14, Mitchell suggested, “The ‘atmosphere’ about military censorship [was] not so good at the present. The press has ganged up on the administration against military censorship with the Military Commission now sitting.”

It would require naval officers “needed for other duties” to appear as witnesses. The jury “would not appreciate the damage of the publication unless it was disclosed at trial that the ‘advance information’ was derived in considerable part from intercepted Japanese messages,” which could dry up sources for naval intelligence.

More embarrassingly, Mitchell wrote, “It is not pleasant to say,” but the trial would show “Johnston got his hands on Nimitz’s secret dispatch or a complete copy of it. If, as appears likely, it may fairly be said there was a much carelessness on ship as the Tribune was guilty of, and the jury may think so.”

Assistant Attorney General Wendell Berge further concluded on July 27, “I do not think this is a case that the public would ever understand. Technical explanation is necessary to spell out the violation, consequently the whole case would become engulfed in questions of freedom of the press, censorship, etc. I do not think we could succeed in making our position clearly enough understood to accomplish any real public benefit.”

What Johnston and Maloney did was “despicable,” however, the “legal grounds for prosecution are too tenuous and the chances of public misunderstanding too great to undertake prosecution.”

The grand jury refused to indict, and ultimately, prevented a trial from happening that would have done great damage to press freedom under the First Amendment.