Police investigating the murder of Syrian-born preacher Abdul Hadi Arwani have arrested a fourth person in connection with his death.
Arwani, 48, was found slumped at the wheel of his VW Passat in Wembley, north west London, on 7 April, with gunshot wounds to his chest.
The father of six was an outspoken critic of Syrian President Bashar al-Assad's regime.
Scotland Yard said a 36-year-old man was arrested on Friday on suspicion of conspiracy to murder.
His arrest was only made public on Sunday (19 April), when he was released on bail.
Two other people remain in custody – a 53-year-old woman held on suspicion of terrorism, and Burnell "Bernie" Mitchell, a 61-year-old man who was previously arrested on suspicion of Arwani's murder and is now being held in connection with terrorism charges.
The investigation took a bizarre twist when it emerged that Muslim convert Mitchell is the brother of Liz Mitchell, the former lead singer of the 1970s disco group Boney M.
Another man, Leslie Cooper, 36, has been charged with the murder of the father-of-six, and is due to stand trial in October.
As part of the investigation, police conducted a search of the An Noor Cultural and Community Centre, a mosque in west London. Arwani was a founding member of the mosque and preached there from 2005 until 2011.
He was previously reported to have been "sentenced to death" in Syria for photographing a site of a massacre in his hometown of Hama in 1982.
The cleric was said to have attended protests against the regime outside the Syrian embassy in London in 2012.
In a statement earlier this week, his son Murhaf Arwani said he wished to thank the police and the Crown Prosecution Service.
"We would also like to thank the community for the outpouring of support during this extremely difficult time," he added. "We are touched to learn how many people my father helped, advised and inspired in his short life.
"If anyone has any additional information that can help with the investigation, we urge you to please come forward and speak to the Metropolitan Police.
"Your cooperation will help us close this painful page and begin to move on with our lives, in the knowledge that the person who took away our father, will be brought to justice and duly punished for this heinous crime."