Police in the UK, who arrested a man accused of hacking FBI computers in the US, are refusing to return his computer because they cannot decrypt its files.
Lauri Love, 30, of Stradishall, Suffolk, who is accused of hacking offences in the US, was arrested in Britain in October 2013.
The National Crime Agency (NCA) searched his home and seized property, before releasing him from bail in July.
Mr Love is now taking the NCA to court after it refused to return items taken.
On 12 March he will petition Bury St Edmunds magistrates for the return of his property.
The BBC understands that the NCA has been unable to decrypt some of the files and does not want to return the computers and media devices until Mr Love helps them to decrypt them.
The NCA told the BBC that as a court case was pending, it would be inappropriate to comment.
Mr Love told the BBC: "Should police, having obtained a reason to acquire information but lacking any overt evidence of criminality sufficient to bring prosecution, be allowed to withhold private data?
"There is a very dire risk that this power will be used to disrupt protected journalistic and political activity."
He said if this "abuse of power" went unchallenged it would set a "troubling precedent".
Mr Love is accused in the US of working with at least three other people - who have not been named - to breach the security of the US military, US space agency Nasa, the Environmental Protection Agency, FBI and the US Federal Reserve computers.
He allegedly worked with "other hackers around the world to gain access".
In July the Crown Prosecution Service said: "The CPS provided investigative advice on the available evidence. The NCA then made the decision to release the man from bail."