An Army private suspected of leaking tens of thousands of classified Afghan War documents has been transferred from Kuwait to a Marine Corps brig in Quantico, Virginia, where he remains in custody.

Pfc. Bradley Manning, a 22-year-old intelligence analyst formerly posted in Iraq, is the focus of a military investigation into the publication of 75,000 secret Army logs sent from Afghanistan between 2004 and 2009. Manning has already been charged over the leaking a video of a fatal 2007 helicopter strike that appeared on the WikiLeaks website in April.

Defense officials said Thursday that they had found concrete evidence linking Manning to the Afghan leaks, but are still combing through computers he used to determine what other material he may have stolen. WikiLeaks is believed to possess another 15,000 sensitive logs.

Manning will remain in confinement as the military continues its investigation and attempts to determine who helped him to provide the documents to the website, defense sources said.