Section 9. Whenever a forest, woodlot or wild-land fire shall have been combatted or extinguished, by the means provided for in this act, the district fire-warden shall prepare a correct statement, showing the date of the fire, the number of men employed to extinguish the fire, the number of hours each was employed, and the actual amount of expense incurred, verified by oath or affirmation, and shall forward the same at once to the Commissioner of Forestry. It shall be the further duty of the district fire-warden thoroughly to investigate the cause or origin of the fire, to collect such evidence as may be discovered relating thereto, and make a report thereon to the Commissioner of Forestry, together with a statement showing the area burned over and damage done by the fire. The assistant fire-wardens shall render their accounts, under oath or affirmation, to the district fire-warden, who shall thoroughly investigate the facts therein stated, and, if he find them correct, shall transmit the same to the Commissioner of Forestry. The above reports and accounts shall be made upon uniform blanks to be furnished by the Commissioner of Forestry.