If it shall appear to the Board of Trustees, after due investigation of such report aforesaid, that such building, walls or structure is in such dangerous condition as aforesaid, the Village Attorney shall notify in writing the owner or owners thereof, by postage paid mailing, directing said owner or owners to put such building in a safe condition or to demolish it. Where, upon diligent search, the identity or whereabouts of the owner or owners of any such building shall not be ascertainable, such notice shall be mailed to the person or persons, in whose name such real estate was last assessed. If after thirty (30) days subsequent to the giving of such notice, said owner or owners fail to put such building in a safe condition or to demolish it, the Commissioner of Buildings or Village Trustees may notify the Village Attorney to initiate proceedings in the Circuit Court of Cook County for an order authorizing the Village to demolish, repair or enclose or to cause the demolition, repair or enclosure of said building.