A man has been arrested on suspicion of conspiracy to murder a Syrian-born preacher found shot dead in a car in north-west London.
Abdul Hadi Arwani, 48, from west London, was found dead on Tuesday in Wembley.
The Syrian-born British national was believed to be a critic of President Bashar al-Assad.
The Metropolitan Police said a 46-year-old man was arrested in Brent in north-west London on Sunday night.
The Met said he was being held in custody at a central London police station.
Counter-terrorism detectives have been carrying out the investigation into the death of the former imam, a father of six.
Mr Arwani was born in Syria and is believed to have attended protests against the Assad regime outside the Syrian embassy in London in 2012.
He had claimed he had been forced to flee Syria in 1982 because the country's regime sentenced him to death for photographing damage in his home city of Hama following government suppression of a rebellion.
Mr Arwani was a preacher at the An Noor mosque in Acton, west London, from 2005 to 2011.
He was found with bullet injuries to his chest in a parked car at the junction of Greenhill and The Paddocks on Tuesday at about 11:15 BST.
Police have said they want to speak to anyone who may have seen Mr Arwani or his car, a dark coloured Volkswagen Passat, that day or on Sunday 5 April.
Officers from the Counter Terrorism Command have discovered Mr Arwani had driven on the Sunday morning near where his body would later be found and parked in Havenwood, where he remained for a short while.
A post-mortem examination found the cause of death to be gunshot wounds. An inquest is due to be opened and adjourned at Barnet Coroner's Court in the coming days.
