Story highlights Bales' attorney says the government is seeking a sanity board review

Prosecutors not cooperating means their case may be weak, the attorney says

A U.S. official tells CNN the exchange of information would come later

The sanity board would examine Bales' mental state

The lawyer for U.S. Army Staff Sgt. Robert Bales, charged with murdering 17 Afghan villagers, said Friday the defense team has been "misled greatly" by U.S. military prosecutors, who have blocked access to information.

John Henry Browne said he was "promised" that witnesses to the incident would be available for them to interview in Afghanistan, "and they were not."

"My staff on the ground is really upset with the promise they made to us," Browne told reporters.

The witnesses have been released from a hospital and were "scattered" throughout the country, Browne said in a Seattle news conference.

"We have no idea where they went, without contact information and without us asking about anything," he said of the witnesses.

Military prosecutors broke trust, he said, and Browne suggested that the military doesn't have much of a case against Bales.

"My gut (feeling) from a defense lawyer's standpoint is when the prosecutors are not cooperating, there's a reason. And the reason is that they don't have much of a case. I don't know whether that's true here or not. But that's true in the past," Browne said. "When prosecutors don't cooperate, it's because they're concerned about the strength of that case."

Earlier Friday, Browne's office issued a statement on behalf of the defense team, accusing the U.S. government of blocking its access to records and witnesses.

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"We are facing an almost complete information blackout from the government, which is having a devastating effect on our ability to investigate the charges preferred against our client," the statement said.

"When we tried to interview the injured civilians being treated at Kandahar Hospital, we were denied access and told to coordinate with the prosecution team. The next day, the prosecution team interviewed the civilian injured. We found out shortly after the prosecution interviews of the injured civilians that the civilians were all released from the hospital and there was no contact information for them," the statement said.

Bales' attorneys said they are also being denied access to the medical records of injured civilians.

"The prosecution is withholding the entire investigative file from the defense team while the potential witnesses scatter into unknown and potentially unaccessible areas in Afghanistan," the statement said.

But a U.S. official told CNN Friday that exchanges of information don't being until Article 32 hearings are ordered. At such a hearing, military authorities would determine whether to proceed with charges against Bales or to put him before a group of experts to determine whether his mental health may be a factor in his defense.

The military investigation is ongoing, and the United States has no jurisdiction over access to Afghan civilians, the U.S. official said.

Meanwhile, U.S. military officials and defense attorneys for Bales are in discussions about a "sanity board" that would examine his mental state, the U.S. official told CNN Friday.

Bales' attorneys were told that convening such a board is likely, the official said. No decision had been reached on whether Bales would be examined at Fort Leavenworth, Kansas, where he is being held, or would be brought to Washington, the official said.

Browne told reporters Friday that "there will be a sanity board review, which we don't control." The government can initiate the review for any reason, and that review could occur in the next two months, which would delay the start of a trial, he said.

Browne said he understood that mental health professionals from Washington would visit Bales in Fort Leavenworth, though those plans could change.

Under the sanity board process, the military command would direct a board of officers to conduct a sanity investigation and hearing into Bales' mental state at the time of the alleged offenses and whether he's competent to stand trial, military lawyer and retired U.S. Navy judge advocate Phil Cave told CNN in a recent interview.

Browne said soldiers have been expressing support to the legal defense team and Bales "a lot more than I'd ever expect."

"He's holding up," Browne said of Bales. "He's seeing a chaplain. The military custodial people are treating him well -- not specially in a good way and not specially in a bad way. But he's being treated well."