In his editing of this passage for the 1837 edition, Joseph Smith changed three instances of hath to has (although the third one was not explicitly marked by him in 𝓟 but probably was made in the 1830 copy that served as the copytext for the 1837 edition). Yet one of these instances of has never made it into the 1837 edition since the 1837 typesetter accidentally skipped from the first “according to the” to the second one. The 1908 RLDS edition restored the missing words “according to the crime which he has committed” to the RLDS text (probably by reference to 𝓟); the 1981 LDS edition restored it to the LDS text. The 1908 RLDS edition and the 1981 LDS edition adopted the change to has because of its occurrence in 𝓟, as emended by Joseph. For further discussion regarding the editing of hath to has, see under INFLECTIONS in volume 3.
Summary: Maintain the restored text in Mosiah 29:15; the 1837 edition accidentally omitted the words “according to the crime which he hath/ has committed”.