A US Air National Guardsman accused of leaking classified military documents has a history of making violent threats, used his government computer to research mass shootings, and tried to destroy evidence of his crimes, federal prosecutors said on Wednesday.

In a 48-page filing, the Justice Department said 21-year-old Jack Teixeira should be detained pending trial, saying his violent rhetoric coupled with his apparent efforts to destroy evidence “compound his risk of flight and dangerousness.”

Prosecutors will present their arguments in favor of detention to a US magistrate judge in Worcester, Massachusetts, on Thursday afternoon.

Teixeira's lawyers have not commented on the case, and are expected to argue at Thursday's hearing that he should not be detained pre-trial.

The filing, which also contained photos of the suspect's bedroom from the FBI's search of his home, said that in July of 2022 he used his government computer to look up famous mass shootings using search terms such as "Uvalde", "Ruby Ridge" and "Las Vegas shooting".

During the search at his home, the FBI found a smashed tablet computer, a laptop and a gaming console inside a dumpster. In addition, prosecutors said they had unearthed evidence that Teixeira instructed other online users to “delete all messages.”

Teixeira was charged earlier this month with one count of violating the Espionage Act related to the unlawful copying and transmitting of sensitive defense material, and a second charge related to the unlawful removal of defense material to an unauthorized location.

If convicted, prosecutors said he faces up to 25 years in prison.

The leaked documents at the heart of the investigation are believed to be the most serious U.S. security breach since more than 700,000 documents, videos and diplomatic cables appeared on the WikiLeaks website in 2010. The Pentagon has called the leak a“deliberate, criminal act.”

Prosecutors said in their detention memo that Teixeira in February 2022 began accessing hundreds of classified documents not relevant to his job, and started posting some of the classified information on social media around December 2022.

"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," the memo says.

The classified documents provided a wide variety of highly classified information on allies and adversaries, with details ranging from Ukraine's air defenses to Israel's Mossad spy agency.

Violent comments

Apart from the evidence that Teixeira tried to obstruct evidence and influence witnesses in the case, prosecutors said he has a troubled history dating back to his teenage years.

When he was 18, they said, his firearms identification card application was denied due to remarks he made while still in high school related to “weapons, including Molotov cocktails, guns at the school, and racial threats.”

He also made violent comments about murder on social media, including one post in November 2022 saying that if he could, he would “kill a ton of people” because it would be "culling the weak minded".

On February 10, 2023, Teixeira sought advice from a user about what type of rifle would be easy to operate from the back of a parked SUV against a “target on a sidewalk or porch,” according to the filing.

Prosecutors said they also found evidence that Teixeira admitted to others online that the information he was posting was classified.

In an exchange of chatroom messages included in the filing, Teixeira was asked whether the information he was posting was classified.

He responded: “Everything that ive been telling u guys up to this point has been.”

In Wednesday's filing, prosecutors said: “There is no condition of release that can be set that will reasonably assure his future appearance at court proceedings or the safety of the community ... He should be detained.”