The lawfully appointed investigator of the District Attorney for the Thirtieth Judicial Circuit shall have the same arrest authority and powers vested in deputy sheriffs of Blount County and St. Clair County while the investigator is performing authorized duties within Blount County and St. Clair County. (Acts 1977, No. 568, p. 757, § 1; Act 80–641, p. 1212, § 1.)