Jack Teixeira, 21-year-old member of Massachusetts National Guard, faces charges in US military intelligence leak case.

Teixeira appeared on Friday in federal court in Boston, Massachusetts, a day after FBI agents descended on his home family home in the small town of Dighton, about 30km (18 miles) east of Providence, Rhode Island.

He was charged with retention and transmission of national defence information and willful retention of classified documents – two criminal offences that could carry up to 15 years in prison, The Washington Post reported.

The federal judge ordered Teixeira to remain in jail. Court documents filed on Friday showed the FBI had used Discord billing information to identify Teixeira.

Following his arrest on Thursday, US Attorney General Merrick Garland said Teixeira had been arrested over the “alleged unauthorised removal, retention and transmission of classified national defence information”.

The Air Force later said Teixeira joined the Air National Guard in September 2019. His official job title was “cyber transport systems journeyman”, a role tasked with maintaining the underlying infrastructure of the Air Force’s “vast, global communications network”.

The leaked classified documents at the heart of the investigation were posted online on a social media website in March and perhaps earlier, but were not widely reported in US media until last week.

Reporting from Washington, DC, on Friday, Al Jazeera’s Kimberly Halkett said the arrest has raised “a lot of questions” about how the relatively low-ranking intelligence official was able to disseminate the information.

“Now, when you have a top secret security clearance in the United States, it is not unusual to be able to have this kind of access,” she said. “But it does give you a large swathe of information.”

US media has reported that Teixeira was the leader of a chat group on the Discord platform that was formed in 2020, and focused heavily on gaming, guns and religion.

He began posting what appeared to be hand-written transcriptions of military intelligence last year, a member of the group told The Washington Post. He later pivoted to posting photos of the documents.

The Bellingcat investigative website has said those photos began to be posted in March, if not earlier.

The leak has roiled the administration of US President Joe Biden, with Pentagon officials saying they were reviewing their policies as they continued to investigate the scale and scope of what had been released.

Authorities have also repeatedly warned that at least some of the documents appear to have been doctored, and may be being used in disnformation campaigns by various actors.

The wide-ranging documents contained US assessments of the war in Ukraine, painting a grim picture that the fighting would likely stretch beyond 2023 and that Kyiv’s air defence faced looming shortages.

The intelligence also appeared to show the extent of US spying on some allies.

Among the apparent revelations, some of the leaked documents appeared to show that Egypt planned to sell weapons to Russia in a deal it intended to keep secret from the US. A senior Egyptian official has denied the report.

Another document seemingly showed that Russian operatives were building a closer relationship with the United Arab Emirates, while a third indicated that South Korean leaders were hesitant to ship artillery shells to Ukraine.

On Thursday, Department of Defense spokesperson Pat Ryder said his agency would not address specifics of the leaked documents as they had not been officially declassified.