"We have determined, based on the findings of this thorough and detailed inquiry, that there is insufficient evidence that the communications between Mr. Clark and Ms. Abdul in any way aided his performance," added the network, which nonetheless declined to release any written documentation from its lawyers' investigation, according to the Los Angeles Times.
The network did say that its new non-fraternization policy is "aimed at preventing any future incidents that could even appear to call into question the relationships between contestants and judges or any other individuals working on American Idol."
The 3-1/2-month inquiry handled by former federal prosecutor Marcell McRae and attorney Ivy Kagan Bierman consisted of interviews with 43 people and a review of material provided by Abdul and Clark.
"I'm grateful this ordeal is over, and I'm so looking forward to getting back to the job I love," Abdul, 43, said in her own statement. "Once again, I thank my fans from throughout the world for their undying love and support."
Clark, whose attorney did not return calls seeking comment on Friday's announcement, had been 1 of 12 finalists during the 2003 second season of Idol when he was disqualified for lying to producers about his criminal record.
Earlier this year, while said to be peddling a book proposal, the 24-year-old had alleged on an ABC Primetime special that he and Abdul had engaged in a sexual affair and that she had helped him select his songs and his outfits for his TV appearances.
"Ms. Abdul acknowledges that she had telephone conversations with Mr. Clark while he was a contestant," said the FOX statement. "Their accounts of those conversations, however, differ greatly and no evidence was uncovered to resolve the conflicts in their accounts."