A Harvard-trained physician said Friday that it can’t be proven conclusively that a Stone Mountain man accused of knowingly exposed women to HIV even has the virus.

Dr. Nancy Banks was one of two medical professionals who testified Friday in the trial of Craig Lamar Davis. He is facing up to 20 years in prison if he is convicted on two counts of reckless HIV, a felony.

Banks, who flew in from Guadalajara, Mexico, also told the court Friday that the Stone Mountain man’s crack cocaine use could have caused him to be wrongly diagnosed with HIV. There are no definitive tests on the market today to determine someone has HIV. The tests look for various proteins that are assumed to be HIV.

“The (current HIV) test is an antibody test,” Banks told The Atlanta Journal-Constitution after her testimony. “They don’t know where those antibodies come from. They’ve never been able to isolate the virus from the protein.”

Banks, who testified on behalf of the defense, was asked to review Davis’ medical records during the time he was alleged to have been diagnosed with the virus. On Thursday, Davis said during his testimony he had used crack cocaine.

“When I looked at the admission history and his physical exam (records), I didn’t think he had a very good history,” Banks said. “The doctor neglected to ask him pertinent questions.”

“What questions?” asked Baron Coleman, an attorney working with the defense.

“Drug use,” Banks said, noting that crack users often develop symptoms such as thrush and certain types of pneumonia that mimic the HIV virus.

“When people smoke crack cocaine, they can develop crack lung,” Banks said. “Hisd X-ray was consistent with that.” She noted that the pneumosistis, a pneumonia often associated with HIV, is usually detected post-mortem. She also said that thrush, a yeast condition also associated with HIV and AIDS, is a side-effect of cocaine use.

Banks and another defense witness, David Rasnick, a pharmaceutical chemist from Oakland, Calif., testified Friday that crack cocaine use can suppress the immune system.

At one point, Banks got into a sparring match with prosecutors over the validity of HIV testing and protocols used to detect the virus that have generally become accepted in the medical community.

Banks and Rasnick were brought in by the Office of Medical and Scientific Justice, a Calif.-based private investigation agency that specializes in criminal HIV cases.

When asked in court Thursday if he had HIV, Davis said that was what he was told by doctors and, therefore, that was what he believed.

Davis has been accused of exposing two metro Atlanta women to HIV. He testified Thursday he did not have sex with the woman involved in the Clayton case but did sleep with the Fulton woman.