The FBI was formed as part of the DOJ and is under the jurisdiction of the DOJ. The FBI reports to both the Attorney General, who is head of the DOJ and the Director of National Intelligence. The DOJ charges the FBI with investigating crimes against the U.S. among other things. The FBI is the investigating arm of the DOJ.
In late 2010, the DOJ stated it was opening an investigation into WikiLeaks and Julian Assange, the site’s founder, to search for potential criminal activity.
According to attorney Barry J. Pollack, the DOJ announced in July it was closing the the criminal investigation (link removed by Me) into (Name Redacted by Me) for her handling of classified information precisely because the FBI could not establish criminal intent. The DOJ made its decision the day after the FBI stated that no reasonable prosecutor would move forward with the case.
For Pollack, this (Name redacted by Me) precedent means that the DOJ needs to close its investigation into Assange, as it seems clear there is no criminal intent, just like the (Name redacted by Me) case. And once that determination was made by the FBI, the DOJ rendered its judgment with speed.
These passages make it clear that both the DOJ and Wikileaks' lawyer, Barry J. Pollack, feel that the FBI is investigating both Wikileaks and Assange and that Pollack feels that investigation has some sort of relationship to at least one other past investigation.