Kim Dotcom says he is about to go on the offensive, after the news that some of the files prosecutors allege Megaupload.com knew were pirated and did not remove were only present because courts had asked they be retained to assist another investigation.

Dotcom's new assault will be based on revelations that megaupload actively co-operated with US authorities on several piracy cases, one of which concerned an outfit named NinjaVideo that used megaupload to store some its files. Megaupload was asked by the US Department of Justice (DoJ) to preserve those files, to assist the ongoing investigation.

Later, the same files were listed among those said to be examples of megaupload hosting pirated files.

The argument isn't that simple, as Megaupload retained the NinjaVideo files, but copies of the same files were also found elsewhere on its servers.

Megaupload's lawyers argue it could not have deleted all the copies of the files in question, as doing so could have damaged the DoJ's case. The DoJ argues that Megaupload's involvement in the NinjaVideo case should have told Dotcom enough about the the provenance of the contentious files to make it obvious they were pirated and therefore worthy of deletion.

Dotcom has taken to Twitter to express his anger about this turn of events, labelling the DoJ “... a gang of rogue US attorneys out of control” and sharing his lawyer's opinion that “We can sue the US govt or MPAA members for $2.6 billion in damages for the destruction of your businesses." Funding to run that lawsuit, he says, is imminent and he looks forward to taking the fight back to the DoJ.

The flamboyant figure has also named a time and date - 20 January 2013 at 6:48am NZ time – the first anniversary of the raid that started the saga, for the launch of his new service. ®