After inspecting the body and hearing the evidence, a jury summoned under this chapter must render its verdict and certify it by an inquisition in writing signed by it, setting forth who the person is and when, where and by what means he came to his death and, if the death was occasioned by the act of another by unlawful means, who is guilty thereof; but if the person, means or manner of his death or the person by whose act he came to his death are not discovered by the evidence, the inquisition must so state, and if there is no evidence tending to show that the deceased came to his death by the unlawful act of another, the inquisition must also state that fact.