DEDHAM, Mass. — Will Karen Read’s dog expert testify at her retrial? That was the focus of a hearing Thursday in Dedham. Dr. Marie Russell testified at Read’s first trial. The defense wants to bring her back, but the prosecution wants to block that.

The Karen Read case returned to court Thursday as a defense expert was on the stand for more than six hours, just so a judge could determine whether or not she can testify at Read's second trial.Dog bite testimony in Karen Read caseNew special prosecutor Hank Brennan filed a motion recently asking Judge Beverly Cannone to exclude expert testimony about an alleged dog attack from Read's second criminal trial.

WATCH LIVE: Karen Read returns to court for hearing on dog bite expert, new retrial date. Cannone is expected to hear arguments in Dedham’s Norfolk Superior Court on whether dog bite expert Dr. Marie Russell will be allowed to testify at Read’s second murder trial.

At Read’s first trial, which ended with a hung hury, the medical expert told jurors that scratch marks on John O’Keefe’s arm appeared to come from a large dog.

Karen Read’s lawyers are pushing back on an effort to block one of their experts from taking the stand in her retrial in April.