A man accused of leaking US military documents had "troubling discussions" about violence and murder and said he was tempted to make an "assassination van", prosecutors say.
The claims have been made as they try to block an expected bid by Jack Teixeira to be released to his father's home while he awaits trial.
The Massachusetts Air National guardsman, 21, disclosed information about the Ukraine war and other sensitive topics in a social media chat room.
He was arrested at gunpoint earlier in April when the information was shared more widely, sparking an embarrassing scandal for defence officials.
They were accused of lax safeguards and faced questions over how someone at a relatively junior level should have access to such sensitive intelligence.
Justice Department lawyers argue Teixeira might still have other information he could potentially expose and that releasing him would be a serious national security risk.
"The damage the defendant has already caused to the US national security is immense. The damage the defendant is still capable of causing is extraordinary," they wrote in court documents.
A hearing on his detention will be held on Thursday at a court in Worcester, Massachusetts.
Lawyers also said Teixeira was a danger to the community who owned multiple guns and had been involved in "detailed and troubling discussions about violence and murder" in the chat room where he shared the documents.
In February, he allegedly told someone he was tempted to make a minivan into "assassination van", according to the documents submitted late on Wednesday.
They also said he had once been suspended from high school after being heard discussing petrol bombs, weapons and racial threats.
A smashed laptop, Xbox and tablet were found in the rubbish at his home, prosecutors added, in an apparent effort to destroy evidence.
People who interacted with the guardsman online have painted him as someone who wanted to show off, rather than having any political or ideological motivation.
Authorities are still to give their view on a motive, and he hasn't yet entered a plea.
The documents shared by Teixeira, who worked as a 'cyber transport systems specialist', included information on battlefield positions in Ukraine and precise numbers for military equipment being supplied by Western allies.