Expert wishes 10-year-old ‘happy birthday’ from stand in Karen Read murder trial

The judge overseeing Karen Read’s retrial on murder charges in the death of Boston cop John O’Keefe cut off the defense’s final witness Wednesday morning after he told jurors he had three children and wished his 10-year-old a happy birthday.

“So I was going to say I have three kids, a 9-year-old who’s actually turning 10 today – happy birthday Kai – and I have two older ones,” said Dr. Andrew John Rentschler, a biomechanical engineer and accident reconstructionist from a firm called ARCCA.

“All right, I’m going to, we’re going to stop this – [use] another example,” said Judge Beverly Cannone after an objection from special prosecutor Hank Brennan.

Brennan has repeatedly tried to have Rentschler’s testimony blocked or limited. The ARCCA scientists dispute the state’s version of events – and have also been accused of destroying text messages with the defense they were ordered to give to prosecutors as well as slow-walking discovery disclosures.

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Andrew Rentschler testifies on the injuries John O’Keefe received when he died at the Karen Read retrial, Tuesday, June 10, 2025, in Dedham, Mass.  (Matt Stone /The Boston Herald via AP, Pool)

Read is accused of mowing down O’Keefe after a night of drinking and leaving him to die as she went to his house and left him raging voicemails as his niece and nephew slept in the home. He had taken them in after they were orphaned when his sister and brother-in-law died within months of one another. 

“Was it appropriate? I think it’s his personality,” said David Gelman, a Philadelphia-area defense attorney and former prosecutor who is following the trial. “It may have missed the mark, but it’s a breath of fresh air since experts are usually boring.”

Grace Edwards, a Massachusetts trial lawyer who is also following the case, said the judge likely cut Rentschler off because narrative answers can distract from the facts of the case.

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Karen Read talks with her defense team before the start of court and the jury is seated during her retrial in Norfolk Superior Court, Wednesday, June 11, 2025, in Dedham, Mass.  (Greg Derr/The Patriot Ledger via AP, Pool)

“The story can lead to a long answer that could be potentially off-topic or the jury could take from it something else that was not intended, like ‘Happy Birthday,’ and only remember that part,” she told Fox News Digital. “The judge wanted the witness refocused to specific questions with focused answers rather than potentially rambling about his three kids.”

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Rentschler insisted that “details matter” repeatedly as he explained the basics of the scientific method and took issue with another expert report from the firm Aperture, retained by the prosecution.

Aperture labeled the injuries to O’Keefe’s arm “lacerations,” he said – a term that he testified contradicts the findings of the official autopsy, which described them as “superficial abrasions.”

Officer John O’Keefe poses for his official headshot. O’Keefe’s girlfriend, Karen Reed, is currently on trial for murder after he was found dead outside of a Massachusetts home in January 2022. (Boston Police Department)

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“The superficial abrasions and abrasions occur when there’s rubbing or scraping of the skin, and it just rubs away the top layer, the epidermis of the skin,” he testified. “Now, a laceration is an actual jagged, ripping or tearing of the skin which gets down through the epidermis into the dermis. So abrasions take much less force. They’re less severe than what a laceration actually is.”

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Dr. Judson Welcher, an accident reconstruction expert, testifies during the murder retrial of Karen Read in Norfolk Superior Court, Thursday, May 29, 2025, in Dedham, Mass. (Mark Stockwell/AP Photo, Pool)

Based on his testing, he said that he ruled out an impact with Read’s 2021 Lexus LX 570 SUV and O’Keefe’s arm as the cause of those injuries.

“They’re inconsistent with striking the taillight or being produced as a result of contact with the taillight,” he testified.

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The prosecution claims that these minor injuries came from an impact with Read’s broken taillight after she allegedly drove into O’Keefe on Jan. 29, 2022 and left him to die on the ground in the snow.

The defense denies a collision and has claimed the injuries came from dog teeth and claws.

Aperture’s Dr. Judson Welcher testified earlier, based on digital forensics of phone and vehicle data, that Read’s SUV reversed at 75% throttle right before O’Keefe’s last conscious interaction with his cellphone.