The suspect uses various aliases, but he was identified to Fox News as Jabir Jubran Ali Al Fayfi

A Saudi once held at Guantanamo Bay has been picked up as part of a larger roundup over the weekend of operatives connected to Al Qaeda in the Arabian Peninsula, a source in Yemen with firsthand knowledge of the arrest told Fox News.

The suspect uses various aliases, but he was identified to Fox News as Jabir Jubran Ali Al Fayfi.

According to defense department documents, he was detainee number 188 at the Navy detention camps.

Fayfi was transferred from the Guantanamo Bay facility to Saudi Arabia in late 2006 after what one official described as a lengthy review.  At the time, Fayfi was considered "low risk" and part of a series of test cases to assess whether the rehabilitation program in Saudi Arabia worked.

He faces conspiracy charges, including aiding and abetting terrorism.

"This is a great test case to weigh whether the government of Yemen is actually serious in their efforts in de-radicalization, and counterterrorism," said Cully Stimson of the Heritage Foundation, who used to run the detainee affairs program and was part of Fayfi's review.

Stimson told Fox News the question this time is whether he is tried, convicted and actually serves his sentence.

Half of the detainees left at Guantanamo are from Yemen.  Analysts question whether the Yemeni government can be trusted to prosecute them in a meaningful way if those detainees are sent home.  In the USS Cole case, a key planner was prosecuted and convicted, but only served two years of a life sentence after a mysterious prison escape.

For context, the Pentagon has not released an unclassified report from last fall on the rate of return to the battlefield or recidivism. Multiple sources confirmed to Fox News that the number of detainee returning to the fight was at least one in five.  For some groups, like the Saudis, Fox News was told the rate of return was much higher.