Convicted killer Michael Johnson used "some sort of metal blade or razor to cut his right jugular vein and an artery inside his right elbow," a Texas Department of Criminal Justice news release said.
Johnson, 29, was scheduled to die by lethal injection at 6 p.m. in Huntsville, Texas, but apparently killed himself at 2:45 a.m., the Waco (Texas) Tribune-Herald reported.
The news release said death row inmates are checked every 15 minutes, and that Johnson had spoken with guards at 2:30 and "made no indications that he was contemplating suicide, nor has a note or other explanation been found."
Johnson was sentenced to death in 1996 by a Waco jury for the September 1995 shooting death of a convenience store worker during a robbery attempt.
The state Office of Inspector General is investigating, the report said.