Authorities are searching for the origin of a mysterious white substance found at a mosque in Perth. Officers quickly rushed to the place of worship on William Street in Northbridge at about 1am on Saturday after reports of a melee outside the building. When officers arrived at the scene, they found a white, 'non-suspicious substance' on the steps outside, 7News reports. WA Police Commissioner Col Blanch said the powder posed no risk to the community. However, he added that the discovery had been concerning. 'We don't know if it was in fact targeted at the mosque, but certainly, given the...