Carroll used a steering wheel lock to hit Tucker on the head a number of times, resulting in severe head injuries.
"I picked up the steering wheel lock and hit him in the shoulder... I hit him again in the shoulder, he went floppy and stopped moving," Carroll told the High Court at Christchurch on Tuesday.
Carroll and Tucker were both involved in the city's drug scene, and the court heard that Tucker had been using fake $100 notes to buy drugs days before his death.
Carroll told the court he started counting the money and the top three notes were real, but the rest were photocopied.
He said he hit Tucker in an effort to intimidate him, but Tucker kept struggling and would not calm down.
When Carroll realised Tucker had died, he and an associate drove out to Lake Ellesmere, wrapped his body in carpet, and set his body on fire.
Tucker's body was found the next day by a group of fishermen and Carroll was arrested six days later.
He was remanded in custody and will be sentenced on November 2.
-NZN