Barack Obama's daughters used to frolic with the other children in the common garden at a gated condominium complex in the Hyde Park area of the South Side of Chicago.

Ann Gottfried, an IT specialist and neighbour whose child used to play with the Obama girls, says that once he was elected to the Senate in 2004, he decided to move out — and up. “He had security concerns. He had a growing family. He has two kids,” she said.

In 2005 the Obamas sold their ground-floor flat at 5450 South East View Park to a jazzman, Kurt Elling, for $415,000, property records show. They moved into a spacious mock-Georgian mansion about a mile away at 5046 South Greenwood Avenue. It was a deal that Mr Obama would come to regret.

Rather than purchase both the house and garden, the Obamas paid $1.65million for the mansion by itself. The garden was sold by the same seller on the same day to Rita Rezko, the wife of Mr Obama's longtime friend and fundraiser Antoin “Tony” Rezko.

Mr Obama's presidential run and Mr Rezko's current trial for corruption have revived interest in the property deal tying the Democratic front-runner to a Syrian-born political fixer.

The candidate has called the transaction a “boneheaded mistake” and donated $150,000 in campaign contributions linked to Mr Rezko to charity. The Obama campaign strongly denies that the Obamas received any discount in the transaction even though Mrs Rezko paid the full asking price of $625,000 for the garden, while the Obamas paid $300,000 below the asking price for the house.

But Mr Obama is coming under pressure to answer lingering questions about the property deal.The Chicago-Sun Times printed its phone number above an editorial headlined: “Sen. Obama, time to call us about Rezko.” Its rival Chicago Tribune opined:“Rezko’s trial now is the background music to Obama’s campaign. And the volume will surely increase before it fades.”

The Obamas bought the mock Georgian mansion in a trust that concealed their identity behind the name Northern Trust No 10209. Bill Burton, Mr Obama's spokesman, told The Times that they did so for “a measure of privacy” and said they were the only beneficiaries of the trust.

The sellers were Fredric Wondisford and his wife, Sally Radovick, both professors at the University of Chicago hospitals, where Michelle Obama served as head of external affairs. Mr Burton said that the sellers and the Obamas were not friends. Mr Burton insisted that Mr Wondisford and his wife had decided to split their property into two lots before the Obamas got involved in the deal.

“I don't recall exactly what our conversations were,” Mr Obama told the newspaper. “I may have mentioned to him the name of [a developer and] he may at that point have contacted that person. I'm not clear about that.” Donna Schwan, the real estate agent who handled the sale, said that the Obamas only wanted the house, not the adjoining garden lot.

But the sellers insisted that the two pieces of property be sold at the same time. A copy of the sale contract shown to Bloomberg News disclosed that the Obamas submitted three bids: $1.3million on January 15, 2005; $1.5million on January 21; and $1.65million on January 23.

Ms Schwan says that she sold Mr Rezko his first condominium when he first moved to the Hyde Park area of Chicago. Court papers revealed that Mr Rezko sought to use his influence to get Ms Schwan an unpaid job on the Illinois Council on Developmental Disabilities in 2003 or 2004. She says that he might have done so because he knew of her work with disabled children.

Mr Obama said that it was “already a stretch” to buy the house and his family could not afford the garden lot as well. The Obamas took a $1.32million mortgage from Northern Trust to help to pay for the house.

The Illinois senator's own financial disclosures suggest, however, that he was prospering at the time. He reported that in addition to his Senate salary he earned $378,239 in book royalties from Dystel & Goodrich and an $847,167 book advance from Random House in 2005.

“With the permission of the Ethics Committee in January 2005, a $1.9million advance against royalties was agreed to by the senator and Random House for writing 2 non-fiction books and 1 children's book ($200,000 of which is to be donated to charity),”

he wrote. “In addition, with the permission of the Ethics Committee, a $370,000 advance against royalties ($40,000 of which had already been previously paid pursuant to the original publishing agreement) was agreed to for work published in 1994.”

Mr Burton said that it would be wrong to view Mr Obama as flush with cash. Mrs Rezko, by contrast, appeared to have very little money of her own with which to purchase the garden lot. The following year, she told a court that she got by on a salary of $37,000 and had $35,000 assets. Prosecutors said last week that Mr Rezko, despite leading an “opulent lifestyle”, was deeply in debt. The following year he told a court that he had “no income, negative cash flow, no liquid assets, no unencumbered assets [and] is significantly in arrears on many of his obligations.”

In a January 2007 court hearing, Mr Rezko told the judge that he already knew he was under federal investigation in 2004 - long before the property transaction involving the Obamas. The Obama campaign said last week that the senator and Mr Rezko viewed the property together.An investigation by The Times determined that three weeks before Mrs Rezko's purchase of the garden lot, Mr Rezko received a $3.5million loan from the British-Iraqi billionaire Nadhmi Auchi, one of Britain's richest men. Mr Auchi, who was convicted of corruption in the Elf scandal in France in 2003, says that the money was a loan for Mr Rezko's pizzeria business in which he was a passive investor.

As well as putting cash down, Mrs Rezko also got a $500,000 mortgage for the garden lot from Mutual Bank of Harvey, Illinois. The Obamas' house is now guarded by Secret Service agents even when the couple are not at home. Mrs Rezko sold a 10ft strip of the garden to the Obamas for $104,500 in January 2006. In December 2006 she sold the remainder to Michael Sreenan, a lawyer for her husband's business, for $575,000.

The garden is now again up for sale for $995,000. It would be cheap at the price if it could make Mr Obama's headache property deal go away.

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