The state fire marshal or his deputy, when in his opinion such proceedings are necessary, shall take the testimony on oath of all persons believed to be cognizant of or to have information or knowledge in relation to suspected arson and shall cause the testimony to be reduced to writing. If he is of the opinion that there is evidence sufficient to charge any person with the crime of arson, he shall cause such person to be arrested in accordance with the law. He shall also furnish the district attorney of the circuit in which the fire occurred with all the information obtained by him in his investigation. The district attorney shall thereupon proceed according to law.