Perth man who tried to rob a Stagecoach bus driver while wearing a blue plastic bag on his head as a mask - and armed with a pair of scissors - was jailed for 20 months at the Sheriff Court.A jury took just 15 minutes to convict 26-year-old Stephen Robertson who had been on remand in Perth Prison awaiting trial on a three-charge indictment.He was unanimously found guilty of attempting to rob Simon Barlow in the city’s Scott Street on May 18, 2020, after boarding the bus, with his face masked,