Scott Wynne confessed in a five-page statement and a 90-minute recorded interview with police, saying he wanted to make amends with the victim's family.
"Although words are inadequate to express my regret for the harm and pain I so thoughtlessly inflicted on the Timmerman family, through this statement I hope to express my sorrow and remorse and provide some closure for them," Wynne wrote.
Timmerman, 37, was killed May 18, 1995, while working in an Allegan Township cornfield after dark. Wynne was convicted six months later. He filed numerous appeals and even convinced a federal judge to order a new trial, a decision reversed by a higher court.
His appeals were exhausted in 2011 with a rejection from the U.S. Supreme Court.
In his statement, Wynne said he was angry that Timmerman had leased his family's farmland, which Wynne considered his own after the death of his father.
He said Timmerman refused to rework a land agreement with Wynne's mother. That night, Wynne painted his face, donned camouflage clothing and approached Timmerman in the darkened field.
Wynne said Timmerman asked, "What the hell do you think you're doing?" and walked toward him. Wynne said he panicked, then became angry and fired a .22-caliber assault rifle. That gun jammed, so he fired repeatedly from a .45-caliber handgun. Timmerman, married and the father of three sons, was hit nine times.
The confession vindicated people whom the defense identified as possible suspects, said Patrick O'Reilly, a retired Allegan County sheriff's detective.
The victim's brothers, Dave and Ken Timmerman, said in a statement: "We were sure all along he was guilty but are glad this is out in the open for the sake of the jury, those that testified, the Sheriff's Department, the Prosecutor, and anyone else that was affected by the tragic event, confirming that the right decision was made."