A doctor testifying as a dog bite expert was cross-examined by prosecutors Tuesday in Karen Read 's second murder trial, as the defense argues she was framed for killing her boyfriend, Boston Police Officer John O’Keefe, and that wounds on his arms came from an animal.

Read, 45, is accused of fatally striking O’Keefe with her SUV and leaving him to die in the snow outside another officer’s home when she dropped him off at a party in January 2022 after the two had been drinking. She's charged with second-degree murder, manslaughter and leaving the scene outside Boston.

Her lawyers say O’Keefe, 46, was beaten inside the home, bitten by a family dog and then left outside as part of a conspiracy by the police that included planting evidence against Read.

A mistrial was declared last year and so far, Read’s second trial has followed similar contours to the first.

A dog bite expert is quizzed

The jury has repeatedly been shown photos of the gashes and scrapes on O’Keefe’s arms, and saw them again on Tuesday.

Prosecutors challenged an assessment by Dr. Marie Russell, a retired emergency medicine physician, who said the wounds on O’Keefe’s arms were the result of a dog attack.

Russell testified Monday she has treated hundreds of dog attacks and bites over nearly 30 years and became interested in the Read case after seeing a news report about questions over whether O’Keefe was attacked by a dog before he died.

“These multiple groupings are patterns and they are, in my opinion, by the teeth and claws of a dog,” Russell said, pointing to a photo of O’Keefe’s arm. She described the wounds as linear and going in a similar direction.

Upon leaving court at the end of the day, Read briefly addressed reporters and said she thought Russell was “fantastic” on the stand.

Prosecutors ask what makes someone a dog bite expert

The prosecution had earlier sought to block Russell from testifying, questioning her credibility. Although the judge allowed her to take the stand, the prosecution renewed their scrutiny and noted Russell never testified before as a dog bite expert and hasn't taken a dog bite forensics course — however she said she was unsure any such certification or training existed.

Prosecutor Hank Brennan asked Russell on Tuesday if there was any universally accepted standard for identifying dog bites. Russell said there was not.

Brennan also pressed Russell about changing her testimony from saying the wounds were caused by “teeth or nails” to specifically naming “canines.”

“When you testified, December 2024, you didn't say nails could have caused these wounds, you didn't say generally teeth, you said canines,” Brennan said.

“I believe that is true,” Russell responded, saying she “became more certain” the wounds were from canine teeth.

Defense calls for a mistrial — again

The defense team leapt on a chance to ask for a mistrial Tuesday after the prosecution pointed out that no dog DNA was found on O'Keefe. The defense said there had been no mention in the trial about DNA and the dog bite, and argued that raising the subject while questioning Russell had prejudiced the jury.

“That cannot be reversed. That cannot be cured. That cannot be ameliorated with a jury instruction,” defense attorney Robert Alessi said while the jury was outside the courtroom.

Prosecutors waved away the accusation, with Brennan saying, “The defense does not get to pick and choose what words the Commonwealth can or cannot use.”

After a brief pause, Superior Court Judge Beverly Cannone said the trial could proceed.

A testy exchange with a former police officer

An exchange on Monday between former Canton police officer Kelly Dever and defense attorney Alan Jackson quickly turned tense after he asked if she wanted to be in the courtroom. Dever said she had “no idea why I’m here,” and later remarked about the defense mispronouncing her name.

Dever testified that while working dispatch on the night O'Keefe died, she could see a video feed from a garage area attached to police department, called a sally port. Read's team has long argued a police cover-up including possibly moving Read's vehicle that was brought into the sally port garage.

Dever said she told federal agents “in good faith” in August 2023 that she saw ATF agent Brian Higgins and former Canton Police Chief Kenneth Berkowitz inside the garage.

However, on the stand she said she realized this wasn't possible because they entered the garage after her shift ended. She attributed the error to “false memory” influenced by media coverage, and said she had retracted her statement.

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