Dmitri Kovtun stayed in a Hamburg apartment
German prosecutors have dropped the case against a suspect in the murder of the Russian dissident, Alexander Litvinenko, in London.
Former KGB agent Mr Litvinenko died in 2006 after he was poisoned with the radioactive substance polonium-210.
Hamburg prosecutors say there is not enough evidence to continue investigating Russian Dmitri Kovtun.
German investigators had suspected him of leaving a trace of polonium in a Hamburg apartment.
Mr Litvinenko, 43, fell ill shortly after taking tea in London with Mr Kovtun and the prime suspect in the case, another Russian, Andrei Lugovoi.
German investigators said Mr Kovtun had travelled to London via Hamburg, where he stayed for one night with his former wife.
They were investigating him on a charge of preparing to commit an offence involving radioactivity.
Explaining the decision to drop the case, the Hamburg prosecutor's office said that, while traces of polonium-210 had been found in the apartment, there was no evidence Mr Kovtun had taken it there.
Alexander Litvinenko died in London in 2006 shortly after being poisoned
Both Mr Lugovoi and Mr Kovtun have said they had nothing to do with the death of Mr Litvinenko.
The British government continues to seek the extradition from Russia of Mr Lugovoi, who has since become a member of the Russian parliament.
Russia refuses, saying the constitution does not allow it, and the issue has strained relations between London and Moscow.
Russia has asserted that Mr Lugovoi was framed by the British Secret Intelligence Service (SIS), also known as MI6.
Senior British officials have said they believe the murder was carried out with the backing of the Russian state.
Mr Kovtun welcomed the German authorities' decision to drop the case, calling it "a triumph of justice".
For his part, Mr Lugovoi told the RIA Novosti news agency: "The new circumstances of the case undermine the whole British investigation.
"Now we demand that the UK objectively investigate the Litvinenko case. Clearly, the act of provocation has failed and it is time that London move from politics to constructive actions."