The prosecution rested this week in the Karen Read retrial after calling their last witness, a crash reconstruction expert who testified about his opinions whether John O’Keefe’s injuries were consistent with being struck by an SUV.
The prosecution’s theory is that Read struck O’Keefe in a fit of rage outside of 34 Fairview Road in Canton in January 2022 and left him incapacitated to die in the snow.
Judson Welcher, an accident reconstructionist and biomechanical engineer, spent three days testifying about his analysis of Read’s Lexus and injuries to O’Keefe.
Welcher testified that his opinion is that the damage to Read’s SUV and the evidence in the case was “consistent with a collision” with O’Keefe. He said that data from her SUV shows she drove in reverse at more than 20 mph outside of the Canton home where his body was found on Jan. 29, 2022.
He also said that the car driving faster than 8 mph and hitting an arm in a sideswipe could’ve cracked the taillight.
Then prosecutors used Read’s own words to cap off their presentation of their case.
Special Prosecutor Hank Brennan has woven interview clips of Read throughout the trial, and he saved one for the end.
Here are the biggest takeaways from the week:
‘That is what happened,’ expert says about SUV, O’Keefe collision

Dr. Judson Welcher, Biomechanical Engineer and Accident Reconstructionist testifies during the Karen Read trial, Tuesday, May 27, 2025, in Dedham, Mass. (Matt Stone/The Boston Herald via AP, Pool)AP
At the end of Tuesday’s testimony, Brennan asked a pointed question about whether Welcher believed, based on his analysis of the evidence, that Read’s Lexus collided with O’Keefe around 12:32 a.m. on Jan. 29, 2022.
“Yes, based on the totality of evidence … that is what happened,” Welcher said.
The defense objected to the question, and the judge ultimately struck the statement from the record. The question then set off a debate between lawyers, but jurors heard Welcher’s answer.
Welcher had gone through the day explaining how he derived his opinion. “Red marks” surrounded the broken cocktail glass in the snow at the scene.
He had played videos of tests he conducted using an “exemplar” Lexus, another way of saying he had bought the same Lexus model that Read had driven that night.
In one test, the Lexus backed up at 2 mph and struck his right arm, bent and holding a cocktail glass. Blue paint on the taillight transferred onto his arm and left a large mark. When compared side by side with photos of O’Keefe’s injuries, they were similar in coverage area.

Judson Welcher, an expert witness, dressed like John O’Keefe and performed crash tests as part of his analysis of the Karen Read case. He testified on Tuesday, May 27, 2025.Court TV
During cross-examination, Welcher said he did not use a crash dummy because he would only have one or two “shots at it” before they damaged the car.
“Pedestrian impacts are so sensitive to initial angles,” he said. “I was not going to hit myself with the Lexus at 20 mph.”
Welcher also pointed out that there was a bruise on O’Keefe’s right knee approximately at the height of the bumper of Read’s SUV. He said the cuts on his arm were consistent with the “geometry and orientation” of the right taillight.
Still, he admitted that a lot of information was still unknown about the physics of the crash.
“We don’t know the exact point of impact,” Welcher said. “We don’t have absolute information to say exactly where he was.”
Based on the car’s data, however, Welcher said that Read’s SUV went three quarters “full throttle” in reverse on Jan. 29, 2022, at around 12:30 a.m. and reached about 23 mph and traveled a total of 87 feet in reverse.
Prosecution seeks to dispel the defense’s theory about Read’s cracked taillight

An impact configuration slide of two SUV’s is projected for jurors to view during the murder retrial of Karen Read in Norfolk Superior Court, Thursday, May 29, 2025, in Dedham, Mass. (AP Photo/Mark Stockwell, Pool) AP
A large part of Welcher’s testimony involved attempting to dispel a theory put forward by the defense last trial.
The issue of when Read cracked her taillight is highly contested. Her lawyers have pointed to a Ring video recorded by a security camera above O’Keefe’s garage as evidence that she could’ve cracked it on the morning of Jan. 29, 2022, before she found O’Keefe.
Neama Rahmani, an attorney and former federal prosecutor based in Los Angeles, said Welcher’s testimony was useful for prosecutors in combatting one of the defense’s big arguments.
“There was also important testimony about the broken taillight and how the broken taillight was consistent with Read hitting John O’Keefe as a pedestrian, and that it was not consistent with an accident with John O’Keefe’s vehicle,” said Rahmani, who’s followed both trials.
In one video from Jan. 29, 2022, before she found O’Keefe’s body, Read backs up and makes contact with O’Keefe’s Chevrolet Traverse. Central to the prosecution’s theory of the case is that Read backed up her SUV and struck O’Keefe, smashing the taillight on his arm in the process.
“Obviously, the defense is arguing that the taillight was broken in another incident with O’Keefe’s car or it was broken when law enforcement impounded the vehicle and towed it in the blizzard,” Rahmani said.
Welcher’s presentation, using a PowerPoint, explaining how the company he works for, Aperture, created digital 3D models of both vehicles using laser scanners along with videos. From the videos and laser scans, Welcher said they figured out “the exact position of the vehicles when that Lexus stopped … and the exact contact.”
“The only evidence of contact is nowhere near the upper taillight,” Welcher said. Using a photograph of O’Keefe’s Traverse, he showed that only a scuff mark remained from when Read’s SUV made contact well below the taillight.
He said that Read’s SUV drove 1 mph or less during the impact with O’Keefe’s car. “That impact did not break or crack that taillight,” Welcher said.
Prosecution rests its case using Read’s own words
A feature of this retrial is the prosecution’s use of video clips of Read’s various media interviews in recent years. None of the videos were played in the first trial.
Brennan, who was hired specifically to try the Read case, has woven video clips in between witness testimony.
“These videos are really hurtful,” Jack Lu, a retired superior court judge, said in an interview last week. After a collection of videos was played last week, Lu said the videos “alone might be enough to convict the defendant.”
After Welcher, the prosecution’s final witness, stepped off the stand on Thursday, Brennan played one final clip.

The prosecution plays a media clip from a docuseries for jurors to view where defendant Karen Read says she asked herself if she could have hit murder victim John O’Keefe during the murder retrial of Karen Read in Norfolk Superior Court, Thursday, May 29, 2025, in Dedham, Mass. (AP Photo/Mark Stockwell/Pool)AP
Here is the full quote Read said in the clip:
So I thought, ‘Could I have run him over?’ Did he try to get me as I was leaving and I didn’t know it. I mean, I’ve always got the music blasting. It’s snowing. I got the wipers going, the heater blasting. Did he — did he come in the back of my car and I hit him in the knee and he’s drunk and passed out and asphyxiated or something. And then I hired David Yannetti, I asked him those questions. ‘The night of January 29, David, what if, I don’t know, what if I ran his foot over, or what if I clipped him in the knee and he passed out and or went to care for himself and threw up or passed out.’ And David [said] ‘Yeah, then you have some element of culpability.’
Defense begins its case
As the prosecution wound down its case in chief, Read told reporters she would put on a fuller and deeper defense during the retrial than she did at her first trial. On Friday, that began with Matthew DiSogra taking the stand.

Accident reconstruction analyst Matthew DiSogra testifies during Karen Read’s murder trial in Norfolk Superior Court in Dedham, Mass., Friday, May 30, 2025. (Mark Stockwell/The Sun Chronicle via AP, Pool) AP
DiSogra is the director of engineering for the Event Data Recorder lab at Delta V and is an expert in vehicle data. His primary role for the defense was not to counter Welcher’s testimony, but to offer a different interpretation of the data taken from Read’s SUV.
While DiSogra relied on the testing of Welcher’s Aperture colleague, Shanon Burgess, he came to a different conclusion. DiSogra told the jury that all the clock variances identified by Burgess created 30 possibilities for when exactly the techstream event identified as a “backing maneuver” happened relative to the last time O’Keefe locked his phone.
It’s critical for the prosecution’s case that the phone was locked before the “backing maneuver” ended, because they claim that maneuver is when Read hit O’Keefe with her car. DiSogra explained that of those 30 possibilities, just three showed the phone lock occurring before the end of the event.
Since DiSogra was called by the defense, Brennan got his first chance to cross-examine a witness. Jurors saw a different side of the prosecutor, whose experience as a criminal defense attorney was evident during the questioning.
Brennan came out swinging.
“Are you trying to offer an opinion suggesting Ms. Read’s Lexus never hit John O’Keefe on Jan. 29, 2022?” he asked. “Is that your opinion?”
The opening question set the stage for what was a thorough cross-examination of DiSogra, during which Breannan sought to undermine the accuracy of some of his conclusions. But Alan Jackson, one of Read’s lawyers, noted on redirect that all of DiSogra’s conclusions were based on the data from Aperture.
The defense will call its next witness when the trial resumes at 9 a.m. Monday.
MassLive reporter Charlie McKenna contributed to this story.