Section 4. If a will has been duly proved and allowed, the probate court shall issue letters testamentary thereon to the executor named therein, if he is legally competent and a suitable person and if he is not under indictment for, or has not been convicted of, murder in the first or second degree, or manslaughter, or accessory before the fact of such crimes, against the deceased and accepts the trust and within thirty days gives bond to discharge the same; otherwise said court may grant letters of administration on the estate as provided in the following chapter.