Fort Meade, Maryland (CNN) -- A convicted computer hacker from California testified Tuesday in Pfc. Bradley Manning's preliminary hearing about six days of chats he conducted with someone who claimed to have leaked classified information and was "looking to brag about what they had done."
Adrian Lamo said he traded instant messages in a chat format with someone self-identified as Bradass87. Lamo testified that based on an e-mail he received from Manning, as well as an examination of Manning's Facebook page, that Bradass87 was Manning.
The testimony came on the fifth day of the preliminary hearing, which will determine if Manning proceeds to a full military court-martial.
Manning is accused of stealing and leaking more than a quarter of a million classified documents from the State Department and the Defense Department to the WikiLeaks website, the biggest intelligence leak in U.S. history.
Army Criminal Investigation Command Special Agent David Shaver later testified that the chat logs that Lamo provided to the Army largely matched chat logs found on Manning's computer in Iraq.
The prosecution did not ask Lamo any specific questions about the chats themselves, but did establish that he was diagnosed with Asperger's syndrome and takes medication for it. At one point he admitted overusing his medication to the point that his parents became concerned and he eventually was put in an involuntary psychiatric hold for three days.
The only possible signs of his medical condition evident in court was his often halting speech and his unusual turn of a phrase. For example, when the prosecutor swore him in and then said "you make take your seat," Lamo responded, "That I shall."
When the defense cross-examined Lamo, he read portions of the chat logs that seemed to indicate that he was not being completely forthcoming with Manning about why he wanted to know details about the leaks.
At one point Lamo wrote, "I'm a journalist and a minister. You can pick either, and treat this as a confession or an interview (never to be published) & enjoy a modicum of legal protection." But Lamo, within a month, had given the chat logs to both Army investigators and Wired magazine.
Before Lamo took the stand, another Army Criminal Investigation Command special agent, Antonio Edwards, testified that Lamo was a confidential informant for the command but was not paid for information. He was reimbursed for normal expenses.
At one point Manning's lead attorney, David Coombs, implied Lamo was asking Manning questions to get him to reveal how he planned to release classified information.
Coombs asked Lamo why he wanted to know, and Lamo replied that he "asked out of curiosity, I am a curious individual. Which has been amply evidenced by my actions."
Because of Lamo's habit of answering yes or no questions with long responses, the cross-examination sometimes got contentious, but not to the point of anyone getting angry or raising their voice.
Near the end, Coombs had to repeatedly ask a question regarding why someone might want to communicate with a minister. Finally both the investigating officer and the prosecutor made suggestions about how Coombs might better phrase the question. It worked. Lamo answered without further problems.
By 3:30 Tuesday afternoon, the prosecution said it was finished presenting witnesses. Coombs plans to call three witnesses starting Wednesday morning.
Testimony on Thursday began with Jihrleah Showman, who was Manning's team leader in the secure computer room in Iraq, as well as earlier, when they were at Fort Drum in New York.
She told of incidents of erratic behavior on the part of Manning that led her to report that she felt Manning shouldn't be handling classified information.
The Army private faces 22 charges, including aiding the enemy. He's accused of stealing and leaking the cables while serving as an intelligence analyst in Iraq in 2009 and 2010.
If convicted on all counts, he could face the death penalty. However, Army prosecutors have signaled they will not recommend death in the event of a conviction, and it is unlikely they would be overruled by a senior officer.
CNN's Charley Keyes and Jethro Mullen contributed to this report