A military panel reached the verdict against Sgt. Vincinte Jackson after several hours of deliberation. The panel of eight Army officers and enlisted soldiers - the equivalent of a jury in a civilian trial - also found Jackson not guilty of premeditated murder. A conviction on that charge could have carried a sentence of up to life in prison without parole.
The sentencing phase began soon after the verdict was read.
During Jackson's court martial, his lawyers conceded he killed 28-year-old Spc. Brandy Fonteneaux of Houston but argued that the slaying was so brutal and random that it couldn't have been premeditated.
In his closing statement, Capt.. Jeremy Horn, one of Jackson's defense lawyers, told the panel that a combination of heavy drinking and a prescription antidepressant left Jackson unable to control his own actions or form any kind of plan to commit murder.
"This is the only theory that makes sense," Horn said.
Horn also said the crime was random because Jackson was trying doors in a corridor and walked in Fonteneaux's room because it was unlocked.
Horn said Jackson was only an occasional drinker but downed three-quarters of a bottle of whiskey the night before Fonteneaux's death.
"Sgt. Jackson was on auto-pilot. ... He felt like he was watching himself," Horn said.
Horn urged the panel to convict Jackson of involuntary manslaughter instead of murder or premeditated murder.
Prosecutor Capt. Jason Quinn scoffed at the defense contention that Jackson was not in control of his own actions.
Quinn said Jackson made a conscious decision to leave his room and walk to Fonteneaux's, where he stood over her while she slept.
"He wants to kill her in that moment," Quinn said.
After stabbing and slashing Fonteneaux, "he decides to reach down and choke her until she is no longer in the misery that he put her in," Quinn said.
Quinn put a photo on courtroom TV screens that showed Fonteneaux after she was killed, sprawled on the floor of her room, partially unclothed with a tangled bedsheet covering part of her body.
"Sgt. Jackson wasn't negligent," Quinn said. "He intended to do what he did. He intended to kill Spc. Fonteneaux."
Jackson, an eight-year Army veteran from Rancho Cucamonga, Calif., was 40 at the time of the killing. He was with the 576th Engineer Company, 4th Engineer Battalion. Fonteneaux was a food operations specialist in the 4th Engineer Battalion.
Fonteneaux knew Jackson but they were not close, according to the aunt who raised her, Bevenly Thomas. Fonteneaux had told her family that Jackson confided in her about his crumbling marriage.
Thomas said she asked Fonteneaux if she and Jackson had a romantic relationship, and she replied, "No, Mom, he's married. He's too old."