Investigators say they've found concrete evidence linking Pfc. Bradley Manning with the "War Logs" ultimately leaked to the Guardian, New York Times and Der Spiegel. From the WSJ:
A search of the computers used by Pfc. Manning yielded evidence he had downloaded the Afghanistan war logs, which span from 2004 until 2009, the official said. It's not clear precisely what that evidence is.
The investigation is also looking at who might have helped Pfc. Manning provide the documents to WikiLeaks, a web-based group that earlier this week released 76,000 secret reports from Afghanistan.