A teen gunman who shot and killed a NSW Police Service employee in western Sydney on Friday acted after he heard a lecture by the extremist group Hizb ut-Tahrir, a local news network has reported. However, the group has downplayed the claim as “speculation”. Seven News said Farhad Khalil Mohammad Jabar was at a talk given by Hizb ut-Tahrir at nearby Parramatta Mosque just hours before he donned a black robe and killed finance worker Curtis Cheng outside NSW Police headquarters in Parramatta. It has also emerged that the shooter’s sister flew out of Australia on a flight bound for the Middle East 24-hours before the terror attack. The gunman has been linked to an Islamist group already under investigation. http://t.co/MitOO7vBxV #7News http://t.co/TYkMqF93HR — 7 News Sydney (@7NewsSydney) October 4, 2015 According to The Sydney Morning Herald, a spokesman for Hizb ut-Tahrir in Australia, Uthman Badar would not comment on the existence of any links between Farhad and his organisation. “Any links are speculation and we could caution against making speculation,” Mr Badar said. Hizb ut-Tahrir rejects democracy, secularism and all Western models of state. On Sunday it held a rally in outer Sydney protesting against military action by Russia and the US in Syria. Parramatta Mosque is believed to have been searched overnight. It sits a few blocks