Denver ? Two days before the start of jury selection in Kobe Bryant’s rape case, prosecutors charged that crucial DNA evidence the defense had hoped to use to prove the NBA player’s innocence might have been contaminated.

The judge in the case granted prosecutors’ request for a hearing today to question the reliability of the defense’s DNA experts. The witnesses are expected to argue that the DNA evidence shows the accuser was promiscuous.

A closed hearing will also be held today to discuss the roughly 100-item questionnaire prospective jurors will fill out.

Prosecutors provided no details about the possible contamination in a court filing released Wednesday. But they expressed concerns about defense expert Elizabeth Johnson, who testified in June that DNA evidence suggests the accuser had sex with another man after her encounter with Bryant and before her hospital examination the following day.

The claim is a core part of the defense’s strategy to undermine the accuser’s credibility and could bolster its claim that she accused Bryant as part of a pattern of behavior intended to gain the attention of a former boyfriend. The woman’s attorneys deny the allegation.

The prosecution did not comment on why it waited until so close to the beginning of the trial to raise the DNA issue.

Prosecutor Dana Easter said contamination was found in DNA control samples intended to ensure accurate testing. That is less of a concern than contamination in samples taken from a defendant or accuser, said Scott Robinson, a defense attorney familiar with the case. But he said it could help prosecutors counter the defense expert’s theories.

“If prosecutors can demonstrate there’s reason to doubt the integrity of the defense lab, that will certainly help,” he said. “With DNA technology, that’s really about all you can do. Juries are so confused by the science involved, you’ve got to attack the evidence.”

Bryant has pleaded not guilty to felony sexual assault, saying he had consensual sex with the woman at the Vail-area resort where she worked last summer.