Almost one year to the day Army investigators arrested intelligence analyst Bradley Manning on suspicion of leaking hundreds of thousands of classified documents to WikiLeaks, the ex-hacker who turned him in is set to meet with the chief prosecutor on the case for the first time.

“I’m finally going to meet with the JAG officer to go over the preliminaries for the actual testimony and how they want to play out my role,” Lamo said in a telephone interview Tuesday. “It’s the first time I’ve met with them.”

The meeting is set for June 2 and 3 in Washington, and marks the first outward sign that Manning’s court-martial case is proceeding apace now that a lengthy inquiry into his mental health has concluded.

The so-called “706 board” had been requested by Manning’s attorney, David Coombs, to determine if his client suffered a “severe mental disease or defect” at the time of his alleged leaking. The board concluded late last month that Manning was mentally fit, clearing the way for an Article 32 hearing — the military equivalent of a grand jury — to determine if a court-martial trial against Manning should proceed.

Manning, now 23, was deployed at Forward Operating Base Hammer in Iraq on May 21, 2010, when he initiated a series of online chats with Lamo. Lamo, who pleaded guilty in 2004 to cracking the internal network of The New York Times, had just been the subject of two stories at Wired.com.

In his first chat, Manning asked Lamo, “If you had unprecedented access to classified networks 14 hours a day 7 days a week for 8+ months, what would you do?”

The conversations continued over several days, during which Manning confided personal problems to Lamo, and claimed that he was responsible for leaking vast amounts of classified material to WikiLeaks, including the “Collateral Murder” video of a helicopter attack in Iraq that WikiLeaks had published the previous month, and a database of a quarter-million U.S. State Department diplomatic cables.

Lamo, who says he was concerned that the leaking might put lives at risk, tipped off the Army and the FBI about Manning’s claims and turned over the logs of their online chats. Manning was seized by Army officials on May 26.

After Wired.com broke the news of Manning’s arrest on June 6, WikiLeaks founder Julian Assange immediately denied publicly that he possessed the diplomatic cables, a position he maintained for nearly six months until he finally began publishing the cache as the “Cablegate” files last November.

Manning is currently facing 22 charges related to illegally downloading information from the government’s classified SIPRnet and passing it to a third party. He has spent most of the last year in maximum security detention under an intrusive “prevention-of-injury” watch. After widespread criticism of the conditions of his confinement — which included prolonged isolation and allegations of punitive treatment by his Marine Corps jailers — Manning was transferred to a pretrial detention facility at Leavenworth, Kansas, last month, where he’s now allowed to mix with other inmates.

Federal prosecutors in Virginia have convened a grand jury in a parallel criminal investigation that’s reportedly targeting Assange. Lamo says he has not testified or been subpoenaed in that probe.

Over the last year, Lamo has had almost weekly telephone contact with a “handler” at the Army’s Criminal Investigation Command, but is uncertain about what will transpire next month when he meets with the chief military prosecutor and a deputy in Manning’s court martial case.

“We haven’t hashed out all of the details yet,” he says. “We’re still at the phase where they’re faxing over the paperwork to approve the expense to place a person in a hotel for one night.”

Manning has become a cause célèbre for the anti-war movement, and Lamo’s decision to report him has made him reviled by Manning supporters and targeted for harassment by the hacker collective Anonymous. Last January, Lamo says an unexpected package addressed to him showed up at his parents’ house in Northern California. The sender was “An Angry Man.”

“We had to have the bomb squad out there to X-ray the package and determine its contents,” he says. “It was a Guy Fawkes mask.”