"He was convicted of murder - not by me, but in a court of law by a jury of his peers - and that can never be erased," Dunne wrote in an article published in the March issue of Vanity Fair.
Kennedy, in an article in the January-February issue of "The Atlantic Monthly," argued that Skakel's conviction stemmed from poor defense work and celebrities such as Dunne and Mark Fuhrman pressuring prosecutors.
Skakel, 42, is serving 20 years to life in prison for beating to death his Greenwich neighbor Martha Moxley in October 1975, when they were both 15. The case remained unsolved for years, until Skakel was convicted in June. His lawyers plan to appeal.
Skakel's father is the brother of Sen. Robert F. Kennedy's widow, Ethel.
Dunne and Fuhrman, a former Los Angeles police detective, wrote books that Kennedy said led to a grand jury investigating the case in 1998. He called Dunne a "driving force" behind Skakel's prosecution.
In his Vanity Fair column, "Dominick Dunne's Diary," the author refuted some of Kennedy's points, including the suggestion that he persuaded Moxley's mother, Dorthy, that Skakel might be involved.
Dunne wrote that in his first conversation with her, he asked her why she was leaving Greenwich.
"She told me, `I couldn't look out my window anymore at the Skakel house. I didn't know who did it, but I knew that in that house someone knew."'
Dunne also challenged Kennedy's assertion that police were not intimidated by the wealthy and well-connected Skakels, saying a former Greenwich police officer told him they were.
Kennedy, reached by cell phone Wednesday, said he hadn't seen the article and could not immediately respond.
The March issue of "Vanity Fair" was released in New York City on Wednesday and will be released nationally next week.