An alleged hacker whose computers were seized by police more than five years ago is using legislation from 1897 to seek their return.
The High Court blocked the extradition of Lauri Love, from Suffolk, to the United States last year.
Mr Love, 34, is alleged to have stolen data from US agencies.
He was arrested and items were seized by British police. Although he was charged in the US, he faces no charges in the UK.
On Monday, Mr Love, who has British-Finnish nationality, is taking the National Crime Agency (NCA) to court.
He is using the Police (Property) Act of 1897 to seek the return of computer equipment that was seized by police in 2013.
The case is being heard at Hendon Magistrates' Court in London.
In 2015, the NCA said it was refusing to hand back Mr Love's computers until he helped them decrypt some of the files.
Mr Love, of Stradishall, said that, as the "NCA has not elected to pursue charges and has seemingly not put any efforts into this end", it is time they returned the property to him.
He said he was concerned at the "absurdly protracted" length of time that he has had to wait for a resolution of the case.
Mr Love, who was arrested in 2013 on suspicion of Computer Misuse Act offences, said it was important to "resist" moves that lead to the "arbitrary deprivation of property and data".
The NCA said the investigation continued and a spokeswoman added: "A number of devices were seized by the NCA at the time, and these devices remain in the hands of the NCA."
Mr Love allegedly stole data from US agencies, including the Federal Reserve, the US Army, the defense department, Nasa and the FBI, in a spate of online attacks in 2012 and 2013.