A Libyan man has been arrested on suspicion of conspiracy to murder PC Yvonne Fletcher three decades ago.
PC Fletcher, 25, died after being shot while policing a demonstration outside the Libyan Embassy in London in 1984.
Scotland Yard described the arrest of the man, in his 50s, as a "significant development".
He was detained on Thursday morning in south-east England and is now in custody. He is also suspected of money laundering offences.
Two other Libyan nationals - a woman in her 40s and a man in his 30s - were also arrested on Thursday on suspicion of money laundering.
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