Lawyers defending a US soldier accused of leaking government secrets say his supervisors failed to recognise his troubled emotional state and revoke his access to classified information.
Private Bradley Manning faces 22 charges of distributing state secrets to whistleblowing website Wikileaks.
On the third day of the hearing, one supervisor refused to testify, invoking his right against self-incrimination.
The hearing is to decide whether Pte Manning should face a court martial.
The charges he faces include aiding the enemy, which carries a sentence of life imprisonment.
On Sunday, army intelligence officer Capt Casey Fulton told the hearing at Fort Meade army base in Maryland that it was impossible to constantly supervise analysts such as Pte Manning.
"There's a limited amount of supervisors and you can't supervise everyone at every second of the day," she said.
"(You) trust that they'll safeguard the material the way they've been taught."
Pte Manning's defence says his closest supervisor, Sgt 1st Class Paul Adkins, failed to suspend his intelligence security clearance despite at least two fits of rage by the private during which he overturned furniture.
However, Sgt Adkins refused to testify on Sunday, invoking his right against self-incrimination as he began answering questions.
Civilian defence lawyer David Coombs argued that Sgt Adkins should not be excused because he was not under criminal investigation. However, the prosecution declined to grant him immunity to testify and he was excused.
Pte Manning, 24, is accused of downloading huge military data files while an intelligence analyst in Iraq and giving them to Wikileaks.
Defence lawyers say Pte Manning was bullied by fellow soldiers and had told his supervisors that he suffered from gender-identity disorder - the belief that he was born the wrong sex.
The hearing heard testimony that Pte Manning was sometimes angry and distant with work colleagues.
Government witness Sgt Chad Madaras said Pte Manning was sometimes sullen and unresponsive, especially toward Sgt Adkins.
"He would sit down at his work station and kind of ignore everyone," Sgt Madaras said under questioning by Mr Coombs.
He said Pte Manning "kind of separated himself from others in the unit".
Pte Manning, from Crescent, Oklahoma, wore camouflage fatigues and dark rimmed-glasses and listened intently to the witnesses, occasionally making notes.
The hearing is expected to run for several more days and the army says it may take several more weeks to decide whether Pte Manning will be court-martialed.