SIOUX FALLS, S.D. (AP) — A Sioux Falls man could spend the rest of his life in prison after being convicted of first-degree manslaughter in the stabbing death of his girlfriend. The Argus Leader reports (http://argusne.ws/1G37LND ) Michael Martinez was found guilty Thursday of three counts of first-degree manslaughter, but was acquitted of second-degree murder and a count of first-degree manslaughter.