Barnett is charged with killing Clay City Police Chief Randy Lacy, who was shot in the back of the head at point-blank range in his police cruiser on Wednesday.
In a jailhouse interview Thursday night with The Associated Press, Barnett said he was too high on drugs to recall any events that led up to the killing.
''I feel like I'm dying inside,'' he said. ''I remember going to a liquor store and eating a handful of Xanax and ending up here.'' Xanax is an anti-anxiety medication.
Investigators were still trying to determine how Barnett was able to grab Lacy's gun. Barnett was handcuffed behind a wire and hard plastic barrier in the back seat of a squad car.
''That's kind of a mystery to us,'' said County Coroner Carl Wells, who conducted an autopsy Thursday.
Barnett, who has scraggly brown hair and a beard and mustache, had tears streaming down his face during most of the interview. He was particularly distraught while discussing his newborn daughter.
''I just want to tell her I love her,'' he said.
He said Lacy was a family friend who had been trying to help him get off drugs. Sometimes at Christmas, the chief even played Santa for Barnett's children.
''I'd lay down there and let them stick a needle in my arm if it would bring him back,'' he said.
Barnett said Lacy, who had arrested him numerous times, would always cuff him in the front ''because he was my friend'' and sometimes didn't handcuff him.
Kentucky State Police acknowledged that Lacy had handcuffed Barnett in the front rather than behind his back -- a frequent practice for suspects he knew.
Greg Adams, a Powell County sheriff's deputy, said Lacy often kept a gun between the seat and console in the front of the squad car. He speculated that the extra gun could have slipped to the back, but state police investigators wouldn't comment on that theory.
Lacy, 55, had served 22 years in law enforcement and was the only active member of the police force in Clay City, a rural town of 1,300 people about 40 miles east of Lexington.
Although the final results of the autopsy weren't available, Wells said Lacy was shot at point-blank range in the back of the head. He was behind the wheel of his cruiser when he was shot, and the car swerved 350 feet before hitting a stop sign and rolling into a ditch, Wells said.
The bullet passed through the back-seat barrier in front of Barnett, whom Lacy had picked up minutes earlier on a charge of driving under the influence.
Barnett has an arrest record dating back to 1993, including multiple drug possession charges. He said he has been high on drugs including cocaine for at least six months and never intended to harm anyone.
''It wouldn't even cross my mind, no matter how messed up I got,'' he said.
Barnett's most recent arrest before the shooting occurred April 9, when he was charged with leaving the scene of an accident, driving with a suspended or revoked license, driving without insurance, DUI and disorderly conduct.
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A citation for the incident reports that he threatened a state trooper by saying, ''Let me out of these handcuffs, I'll hurt you.''