Defense attorneys sparred with federal prosecutors Friday over testimony by a medical expert on the fourth day of Dr. Joel Sabean’s fraud trial in U.S. District Court in Portland.

Attorneys for the prominent South Portland dermatologist worked to undermine Dr. Gary Hatfield’s testimony as he cast doubt on Sabean’s claim that he sent a family member millions of dollars over a five-year period because he believed she needed treatment for an array of medical ailments ranging from kidney stones and heart surgery to a kidney transplant and multiple toe amputations.

Prosecutors pitted doctor against doctor, guiding Hatfield, an internist who once chaired the state’s medical licensing board, through a series of emails Sabean sent between 2007 and 2011 requesting funds to pay for the family member’s many medical treatments. Hatfield testified on the severity of the procedures Sabean claimed the woman was undergoing, the likelihood she would receive the described treatments, sometimes in quick succession, and whether Sabean was qualified to diagnose and prescribe controlled substances to a family member who lived 1,500 miles away.

In his testimony, Hatfield said Sabean’s description of the woman’s medical history did not seem credible.

“To have all these illnesses over this period of time did not make sense,” Hatfield said.

Prosecutors allege that Sabean, who lives in Falmouth and has had a successful dermatology practice in South Portland for nearly 40 years, sent the woman money to cover up a sexual relationship she said began when she was 12 or 13.

Sabean, 69, is not charged with sexual abuse. The Portland Press Herald does not name victims of sexual abuse without their permission.

He is charged with falsely claiming more than $2 million in medical deductions to avoid paying nearly $900,000 in taxes, as well as illegally distributing controlled substances by prescribing the woman anti-anxiety and sleeping medications, and health care fraud for writing some of those prescriptions in his wife’s name so the costs could be applied to their insurance.

Defense lawyers poked holes in the medical expert’s testimony, arguing he had not been informed of Sabean’s previous experience, including time as a pediatrician and emergency room physician, given the woman’s full medical history or seen her medical records before giving his opinion.

Questioned by defense attorney Alfred C. Frawley IV, Hatfield allowed that Sabean would have been able to monitor the woman’s prescription use if he had spoken with her regularly, though Hatfield maintained that Sabean should not have prescribed medication to a family member for an extended period.

In previous days the woman, who is the star witness for the prosecution, testified to fabricating medical bills to help Sabean justify the payments after his wife and co-workers became suspicious, creating invoices using logos she found on the internet and medical codes largely provided by Sabean.

The woman, who is now 41, admitted to having “a problem lying my whole life.” She is serving a jail sentence in Florida for falsifying community service records after being sentenced for shoplifting.

Defense attorneys expressed frustration over U.S. District Judge George Z. Singal’s decision not to allow evidence they say would have further undermined the woman’s credibility.

“When the judge keeps your evidence out, it’s very hard,” said Jay McCloskey, one of Sabean’s attorneys, during a break in the proceedings Friday.

On Friday the woman, wearing a red prison jumpsuit, broke down on the stand, saying she still loved Sabean, despite years of sexual abuse.

“This is the worst and most horrific thing I’ve done in my entire life,” she tearfully told defense attorneys, before being excused.

Prosecutors also called Sabean’s accountant, Joel Bassett, to the stand, walking him through several tax returns his firm helped prepare for Sabean and showing emails Bassett sent to Sabean’s bookkeeper inquiring about records for requested medical deductions. Bassett will continue his testimony on Monday.

Defense attorneys say they expect the trial to continue through next week.

Correction: This story was updated Nov. 5 to clarify details about Dr. Sabean’s emails and the family member’s testimony during trial.