Defense rests after biomechanics expert testimony in Karen Read retrial

Flint McColgan, Boston Herald on Jun 11, 2025

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DEDHAM, Mass. — Karen Read’s defense rested its case after calling 11 witnesses, with three of the last four being experts who testified that in their examination a vehicle strike could not have killed John O’Keefe.

Read, 45, of Mansfield, faces charges including second-degree murder in the Jan. 29, 2022, death of O’Keefe, her boyfriend and a Boston Police officer. She was tried last year on the same charges but that ended in a mistrial.

The jury will have Thursday off as attorneys prepare for closing arguments on Friday. Prosecutor Hank Brennan said that he “will not be calling any witnesses or putting on any further evidence” now that the defense has rested.

“There was no bruising, there was no laceration, there was nothing at the alleged point of contact which would indicate an impact that produces thousands of pounds of force on the arm,” Andrew Rentschler, a PhD senior biomechanist with the engineering consultancy ARCCA, testified Wednesday, his second day on the stand. “No evidence for it whatsoever.”

Similar conclusions were reached by Rentschler’s ARCCA colleague Daniel Wolfe and Dr. Elizabeth Laposata, a former chief medical examiner for Rhode Island who now does consulting work.

Each examined the evidence through their own specialty lens and further highlighted the high technicality of the case. The defense nearly doubled the number of witnesses they called from six last year to 11 this year, and did without a digital forensics examiner to argue their case about a controversial web search for “hos long to die in cold.”

Wolfe, the PhD chief of ARCCA’s accident reconstruction unit, and Rentschler testified for the defense last year that regardless of any other factors or context, the facts of the vehicle damage and O’Keefe’s wounds do not support a vehicle strike.

They reached the same conclusion this time but spent a lot more time challenging the methodologies and conclusions of the prosecution’s own final witness, Judson Welcher, another PhD at rival engineering consultancy firm Aperture.

Welcher’s testimony was largely a walkthrough of his PowerPoint presentation, which included a test where he painted the right taillight of a Lexus just like Read’s. He then had himself struck in reverse at slow speed and looked at the paint transfer to see where the vehicle may have struck O’Keefe’s arm.

By the end of Welcher’s first of three days on the stand, prosecutor Hank Brennan asked him if his testing supported the theory that Read’s Lexus LX570 struck O’Keefe at around 12:32 a.m. on Jan. 29, 2022, outside 34 Fairview Road in Canton?

“Yes,” Welcher said. “Based on the totality of the evidence, DNA, everything I’ve talked about, that is consistent with that happening and within a reasonable degree of scientific certainty that is what happened.”

Wolfe and Rentschler both contested that claim, with Rentschler saying of Welcher’s presentation, “I’m not sure what that test actually accomplished or presented.”

During the final witness showdown, Brennan upped the heat of his cross-examination of Rentschler, continuously questioning him about what he did or did not consider during his review of Welcher’s test.

He also suggested that Rentschler’s testimony was informed by outside influence that was barred by court order, asked questions designed to remind jurors that ARCCA was being paid.

“Are you giving your opinion or are you regurgitating what you read in a report?” Brennan asked during one lengthy exchange.

The lines often drew objections by defense attorney Alan Jackson who at one point asked Judge Beverly Cannone that Brennan be “admonished” for “editorializing.”

But Rentschler repeatedly fired back that the evidence does not back up the prosecution’s claims of how O’Keefe died and that some of the specifics Brennan asked about were either irrelevant to the analysis or were unknowable.

As an example, Brennan asked if he knew how O’Keefe was standing when he was allegedly struck by the vehicle. Rentschler said, “No. Nobody knows.”

In a rare lighter moment Wednesday, Rentschler wished one of his three children a happy 10th birthday from the stand while explaining the scientific process. The example drew an objection for being too personal and he was asked to move it along.

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