The family of a Syrian imam who was shot dead on a London street have paid tribute to 'the most peaceful man you could ever wish to meet' as counter-terror police continue to investigate his murder. Abdul Hadi Arwani, 48, a fierce critic of president Bashar al-Assad, may have been assassinated by the governing regime in his home country, according to friends. The father of six was found slumped in a Volkswagen Passat with wounds to his chest on a street in Wembley on Tuesday morning. Last night it emerged that Metropolitan Police counter-terrorism officers, who handle political assassinations, were now leading the inquiry because of its potential 'international dimensions'. Scroll down for video . Outspoken: Abdul Hadi Arwani had taken part in a demonstration against President Assad three years ago . His son Murhaf issued a statement on behalf of the family, calling for witnesses to come forward and paying tribute to the political dissident who fled Syria after being apparently sentenced to death by Assad's father. 'My family and I have been in a state of shock ever since we learned of this terrible news,' he said. 'We have not slept and our minds are a blur as to what happened and why. 'The police are currently investigating this brutal murder. As an individual, a family and a community, we are helping the police to solve this heinous crime.' Murhaf continued: 'He was the most peaceful man you could ever wish to meet. He just loved to help people. He did not care what your background, race or status was. 'He did not care if you were rich or poor. He just wanted to help people in need. 'He was an old fashioned man who thought love and understanding could cure all of the world's ills. He was always smiling and joking with everyone he met. 'He showed so much love to his congregation and to his community as an imam and a loving father to us, his six children. I don't know how we will cope without him.' Imam: Mr Arwani was a preacher at the An-Noor Mosque (pictured) in Acton, West London, which has a reputation for hosting fundamentalist speakers . The statement said Mr Arwani was a 'peaceful man' who was 'actively involved in the fight against extremism'. 'He spoke up and out against the crime of terror and oppression wherever he found it,' it said, adding that Mr Arwani was 'a British citizen who loved the people of this country'. Murhaf added: 'He loved the idea of democracy and freedom. He loved the idea of freedom for all regardless of religion, race and background.' A source has claimed that the killing had all the hallmarks of a 'state-sponsored assassination', while a friend laid blame at the feet of 'Assad and his cronies'. Last night, the Metropolitan Police said detectives from its counter terrorism command are carrying out the inquiry 'because of their expertise in the management of investigations with international dimensions and an established liaison network abroad'. Mr Arwani was an imam at the An-Noor Mosque in Acton, West London, but was forced to step down last year over reports it was repeatedly linked with extremists. He was found with gunshot wounds to his chest in Wembley on Tuesday morning. He was declared dead half an hour later. His daughter Elham Arwani said her father ran a building company and had been visiting Wembley in connection with his work. Speaking from the family home yesterday, the 23-year-old said: 'We have no idea what happened. We don't even know how he was killed. We have just been told he was killed and that's it. 'Any Syrian who is free and who knows the truth is against Assad. It's not going to be because he was against Assad. It must be for another reason, but we can't think of anything.' She described her father as a 'loving father and husband' and added: 'He was the best person, always helping everyone. His phone would ring 24/7 with people asking for help and advice.' At least 200 mourners gathered to pay tribute to him last night at Nadi Park Royal in Willesden Junction, north west London, where he preached every Wednesday. Preacher: Mr Arwani was known for his outspoken opposition to the Assad regime . Mourners claimed the  imam was a peaceful man who opposed extremism. Some speculated that he may have been killed in a hit from the Syrian regime or because of a disagreement over management of the west London mosque. One also said that he had visited Syria 10 times in recent years but had been ordered by the Turkish government to stop and had been questioned by security services at an airport there. Dr Khaled Kamaraldi, who gave Arwani his first job as a builder 15 years ago, said: 'He went out to Syria to educate the fighters about the treatment of prisoners of war and about human rights. 'He said if you behaved like the Assad regime you become like them. He was questioned by security services but they let him go. He said everything in his heart.' He added: 'This was a state kill. Assad was behind it, and if not Assad one of his cronies. He was very active against the Assad regime. But he was a conciliator, he was not violent. 'What shocks me is they shot him in broad daylight in the centre of London. They have no respect. There is no doubt the police will get him.' Home: Mr Arwani, originally from Syria, lived in this home in White City, west London . One friend, solicitor Mohammad Bassam Tablieh, 43, from west London, said there could be 'two reasons behind his killing'. He said: 'Number one: a dispute about running the mosque. Number two: his activities against Assad. He was an active member of the opposition against Assad. 'There was a problem with dealing with who is imam at the mosque. He had nothing to do with extremism at all he was a very moderate person, very peaceful.' He added that many people in London who had green flags in there car as a symbol of being anti-Assad have had their tyres slashed but did not know if Mr Arwani had one in his vehicle. But Haras Rafiq, managing director of anti-extremist think-tank the Quilliam Foundation, said it was too early to start speculating about why Mr Arwani was killed. He said: 'He was definitely anti-Assad, he was very vocal and we all know that. But he wasn’t necessarily Assad’s biggest enemy here in the UK. I am just thinking "Why him?" and not other people that we know are more vocal and more active. 'They have got other problems, more serious problems in Syria. If the murder was carried out on behalf of Assad, then that would suggest that they are looking at people abroad, but it is not something that I have come across.' Mr Rafiq added: 'Arwani himself wasn’t actually extremist. He wasn’t on my radar as somebody who himself held extreme hatred-based views. However, the centre that he was involved in was quite controversial.' Mr Arwani was involved in violent anti-Assad demonstrations outside the Syrian Embassy in London in 2012 . Mr Arwani grew up in Hama, the site of a notorious 1982 massacre where up to 40,000 civilians were killed by the Syrian Army under the orders of Hafez al-Assad, the current president's father. In a lecture he gave in 2012, Mr Arwani described how the Assad regime had sentenced him to death, forcing him to flee his homeland, and then harassed his elderly relatives for three decades. Mr Arwani, who was just 16 at the time, said that he took a series of photographs chronicling the damage done to mosques and houses in the city, and was sentenced to death by the authorities for it. 'When they found out that I did that, they issued a capital punishment against me, when I was 16 years old - so I had to flee from Syria,' he said. The teenager bribed a policeman so he could leave the country, he said - but for the next 30 years, the authorities questioned his parents once a month in an attempt to find out where he had gone. Mr Arwani blamed the atrocities carried out by the Assad regime on its supposed abandonment of Islam, saying that from the 1960s the government 'started to implement atheism, and take off Islam from the life of the people'. He also claimed that Muslim scholars were forced to stop working as imams, and told to take jobs selling cosmetics instead. The Assad regime has been known to assassinate its political opponents in the past, most prominently the Lebanese prime minister Rafik Hariri, whose killing in 2005 was blamed on the Syrian government. The An-Noor Mosque, where Mr Arwani used to be one of the main imams, has a reputation for hosting fundamentalist speakers. The mosque became notorious in 2013 when a terror suspect went there and changed into a burqa in order to escape surveillance then went on the run. Mohammed Ahmed Mohamed has been missing for 16 months, and was last seen entering An-Noor dressed as a man before leaving in a full-length covering designed for women which obscured his identity. He was subject to a Terrorism Prevention and Investigation Measure, which restrict the movements of people suspected of involvement in terrorism. Other extremists linked to the mosque include Uthman Mustafa Kamal, the son of hate preacher Abu Hamza, who has regularly led prayers at An-Noor. Three years ago, another preacher delivered a sermon arguing that 'Jews, Zionists, all of those people' who mock the prophet Muhammad deserve to face 'the sword'. Some friends of Mr Arwani said that he had left the mosque after a dispute about money, despite reports that his departure was linked to extremism . Ali Belai said: 'Nothing he said was ever extremist. The management forced him out of the mosque. There was conflict over money. I think it was about £30,000.' Anas Qamar, another Syrian exile, said that Mr Arwani had been involved in a High Court battle over the mosque's finances when one of the trustees allegedly embezzled money from worshippers. 'Abdul Hadi said the mosque was a charity and should not be run to profit one man,' he said. 'He was banished by the mosque.'
Abdul Hadi Arwani was found dead in on a street in Wembley on Tuesday .
Counter-terror police are investigating claims he was assassinated by the Assad regime in Syria .
Family paid tribute to him claiming that he loved British democracy .
Mr Arwani was a preacher at  London mosque with extremist links .