British counterterrorism detectives say they've arrested a fourth person as they investigate the slaying of a Syria-born Muslim cleric who was shot in London.

Scotland Yard's Counter-Terrorism Command said Sunday a 36-year old man was arrested on suspicion of conspiracy to murder Abdul-Hadi Arwani and was released on bail.

The 48-year old former imam at the An-noor mosque in west London was found with gunshot wounds in a parked car on April 7.

A 61-year-old man was arrested on suspicion of conspiracy to murder and on suspicion of commission, preparation and instigation of acts of terrorism.

A 53-year-old woman was also arrested on the terror charge. No details were offered as to what the terror charges entailed.

Another man, Leslie Cooper, 36, was charged with the murder.