COLORADO SPRINGS, Colo. — Smoking a cigarette outside his barracks, Sgt. Vincinte Jackson turned to a  Fort Carson specialist earlier this year and asked how he’d kill someone, the  specialist said.

About 24-hours later, Jackson stood over the lifeless body of a woman in his  battalion — the death a result, a forensic psychologist testified, of a potent combination of alcohol and anti-depressant pills.

Whether Jackson intended to kill Spc. Brandy Fonteneaux in January dominated  testimony in the sergeant’s court-martial on Tuesday, when the Army prosecutors  that charged him with premeditated murder turned the case over to his defense  attorneys.

Shortly before the killing, Jackson was cleared for retirement by a medical  board, witnesses said. Jackson suffered a shrapnel wound in Afghanistan.

Declaring Jackson’s mental state the “point of this trial,” Capt. Jeremy  Horn, a defense attorney, focused largely on testimony from Gail Poyner. The  Oklahoma City-based forensic psychologist quoted studies and research on the anti-depressant Jackson consumed that night, along with at least two-thirds of a  bottle of Crown Royal whiskey.

“I strongly believe that Celexa is the approximate cause of this crime,”  Poyner said.

She testified after prosecutors relentlessly questioned her credentials. She  has a doctorate in psychology from the University of Oklahoma, but Poyner said  she isn’t certified through several trade associations, including the American  Board of Forensic Psychology.

Prosecutors also questioned her lack of schooling in biology, chemistry and  physiology after she received her associates degree. She said it wasn’t a  requirement.

The court-martial recessed for the day before prosecutors could cross examine  her.

Earlier Tuesday, Capt. Jason Quinn, a prosecutor, called his last witness — a  former soldier who spoke of the conversation he had with Jackson while the two  smoked cigarettes one day before the killing.

When asked by Jackson how he’d kill someone, Nryk Stewart said he’d use a  gun. The answer confused Jackson, Stewart testified.

“You wouldn’t think about cutting them?” Jackson told the former soldier.