The millionaire heir to the fortune of the American chemical company DuPont has escaped prison after raping his three-year old daughter because a judge considered he wouldn't "fare well" in prison.

Robert H Richards IV pleaded guilty in 2008 to fourth degree rape, which usually carries a 15-year sentence in the US, but a Superior Court judge suspended his eight year sentence because she considered he would not "fare well" in prison, The News Journal reported.

Judge Jan Jurden ruled Richards needed treatment and noted that child molesters are often targeted by other inmates in prison. Richards won't serve jail time unless he violates his probation.

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The rape case made headlines earlier this month after Richards' ex-wife filed a lawsuit seeking compensatory and punitive damages for assault, negligence, and inflicting emotional distress on his two children, after claiming he also abused their 19-month-old son around the same time.

In a news conference, her lawyer, Thomas Crumplar, said: “Making matters worse this self-admitted rapist and child abuser has not paid a single penny to these children for his crimes. There is no provision whatsoever for them for their future after they turn 18.”

According to his arrest warrant issued in December 2007, detective JoAnna Burton noted the girl told her grandmother she didn't want "daddy touching me anymore".

The child said Richards sexually abused her in her mother's bedroom and her brother's room in his $1.8 million mansion. Richards told her it would be "our little secret".

Richard’s wife told the police her husband admitted to abusing the girl but said it was an "accident" and promised "not to do it again", according to the warrant reportedly seen by the Delaware-based News Journal.

Richards was freed on a $60,000 bail while awaiting charges and was offered a plea to a single count of fourth-degree rape carrying no mandatory jail time, which he later accepted, admitting in court that he abused his own daughter.

Richards was placed on Level 3 probation for eight months, which requires weekly contacts with a probation officer, before Judge Jurden placed him on Level 2, which only requires a monthly visit with a probation officer.

Richards is unemployed and lives off his trust fund. He is a relative of the DuPont family and the son of Robert H Richards III, a partner at the Richards Layton & Finger corporate law firm.