Con man or crackpot?

A jury will have to decide whether a man who calls himself Clark Rockefeller was legally insane when he ran off with his 7-year-old daughter during a supervised visit or whether he is a consummate schemer who used aliases to insinuate himself into highbrow circles in Boston, New York and Los Angeles, culminating in a well-orchestrated kidnapping.

His trial is set to begin Tuesday in Suffolk Superior Court.

Rockefeller's real name is Christian Karl Gerhartsreiter. In July, he grabbed his daughter, Reigh, during a supervised visit in Boston, pushed a social worker who was watching them and fled in a waiting car. He and the girl, nicknamed "Snooks," were found six days later in a $450,000 Baltimore condominium he had bought two weeks earlier.

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His attorneys are planning an insanity defense, saying he is not criminally responsible because of long-standing psychological problems, including bipolar disorder and depression.

The defense is most often used in murder cases, and is rarely successful. But given the nature of the charges, some defense lawyers not involved in the case think he could succeed.

"When you get down to it — despite all the publicity of this case — it is a parent taking a child without permission," said Boston defense attorney Peter Elikann. "While that's certainly a serious matter, it's not on the level that insanity defenses are usually used. There are jurors out there who may have some sympathy for his position as a heartsick parent."

Prosecutors, however, say he was perfectly sane. They describe him as a longtime con man who carefully planned the kidnapping months in advance.

"(He) is at the center of the longest con I've ever seen in my professional career," Suffolk District Attorney Dan Conley said shortly after his arrest.

Gerhartsreiter is not a descendant of John D. Rockefeller, the famous oil tycoon, but police say he wanted people to believe that. Instead, he is a German man from a modest upbringing in Upper Bavaria who moved to the United States more than 30 years ago.

Since then, authorities say, he reinvented himself over and over again, becoming:

—A German student who lived with families in Connecticut.

—A 19-year-old husband who left his Wisconsin bride a day after they married.

—An aspiring actor named Christopher Chichester, who told friends in California that he was a descendant of British royalty.

Authorities say he has called himself Clark Rockefeller since about 1993 and claimed various professions, including physicist, mathematician and art dealer.

Even his wife, Sandra Boss, a Harvard Business School graduate, didn't know his true identity.

Authorities haven't said when she realized he was not who he said he was. But after she became aware of his aliases, she asked a judge to restrict his access to their daughter. As part of their 2007 divorce, he received a settlement of $800,000 and agreed to three supervised visits with the girl each year.

Boss, who is now a senior partner at the London office of the management consulting firm McKinsey & Co., is expected to be a key prosecution witness.

In jailhouse media interviews, Gerhartsreiter, 48, insisted his name is Clark Rockefeller and claimed he couldn't remember much of his childhood. He portrayed himself as a doting father who cared for his daughter full-time while the family lived in a mansion in Cornish, N.H., and a $2 million brownstone in Boston.

He told police he was distraught over losing custody.

In addition to a parental kidnapping count, Gerhartsreiter faces a charge of giving a false name to police. He also faces two assault and battery charges for allegedly pushing the social worker to the ground and then instructing a limo driver to take off as the social worker tried to climb into the car. The social worker suffered minor injuries.

Prosecutors, to bolster their argument that Gerhartsreiter methodically planned the kidnapping, say two real estate agents from Baltimore are expected to testify that he first contacted their firm more than six months before the kidnapping, saying he was looking for a home for him and his daughter.

Gerhartsreiter's lawyers are hoping the jury won't hear much about his past or the various aliases he has used.

They've asked the judge to bar prosecutors from mentioning a grand jury investigation in California, where Gerhartsreiter is a "person of interest" in the disappearance and presumed slayings of Jonathan and Linda Sohus, a newlywed couple from San Marino. He has denied any role in the couple's disappearance.

Two defense experts will testify that Gerhartsreiter has "issues of identity," and symptoms of "delusion and grandiosity," according to court documents.

Boston defense attorney Joseph Balliro Sr. thinks the insanity defense might work.

"He fancies himself a Rockefeller — there's no justifiable reason for that, other than having some kind of psychosis," Balliro said. "Together with the fact that he never injured this child — there's no suggestion that he had anything but love for her — and I think he's got a reasonable opportunity."