abdul hadi arwani was found in the back seat of his black volkswagen passat on tuesday morning in wembley , north west .
the 48-year-old syrian national was an outspoken critic of the assad regime and ` actively ' campaigned against extremist , his family have since revealed .
on monday morning scotland yard confirmed that a 46-year-old had been arrested in brent , north west london , on suspicion of conspiracy to murder .