London (AFP) - A Libyan man suspected of killing a British police officer during a 1984 London protest against Moamer Kadhafi was released Tuesday because evidence against him could have breached national security.
The suspect, aged in his fifties, was arrested in November 2015 as part of the long-running investigation into the murder of Yvonne Fletcher.
The 25-year-old female officer was killed while policing what had been a small and peaceful demonstration outside the Libyan embassy in London.
Her family said they were "deeply disappointed and frustrated" at Tuesday's news.
Supporters of Kadhafi -- the longtime Libyan dictator who would be killed in 2011 -- were holding a rival rally on the same day and "a number of shots were fired" from within the embassy, police said. Fletcher was fatally hit in the back.
The Metropolitan police said that although "enough material to identify those responsible" had been identified, it could not be presented in court.
"The key material has not been made available for use in court in evidential form for reasons of national security". After a review prosecutors decided there was "insufficient admissible evidence to charge the man".
In a statement released by police, Fletcher's family expressed regret.
"We had hoped that the latest turn of events would finally lead to some closure for the family," they said.
The killing of a woman police constable caused deep public revulsion and sparked an 11-day standoff with police outside the embassy, officially referred to as the Libyan People's Bureau.
It led to Britain severing diplomatic relations with Libya until 1999 and has long been an obstacle in ties between London and Tripoli, along with the bombing of Pan Am flight 103 over the Scottish town of Lockerbie in 1988.
In 1999, Libya accepted "general responsibility" for Fletcher's death.