Section 8. If property of the value of fifty dollars or more is destroyed or if property is damaged to that amount or to a value in excess thereof by fifteen or more persons who are riotously or tumultuously assembled and provided that the activities of such riotous or tumultuous group are observed and reported to the police during the period that such activities are occurring, the town within which the property was situated shall, if the owner of such property uses all reasonable diligence to prevent said destruction or damage and to procure the conviction of the offenders, be liable to indemnify the owner thereof in tort to the amount of three-fourth's of the value of the property destroyed or of the amount of such damage thereto, and may recover the same against any or all of the persons who so destroyed or damaged such property.