At the heart of the murder charge against Karen Read is the weapon prosecutors say she used to kill her boyfriend — her 2021 Lexus SUV.

Prosecutors spent much of the fifth week of the widely publicized retrial laying out the physical evidence that they say shows that Read drunkenly drove into Boston police officer John O’Keefe, 46, and left him for dead outside the home of a law enforcement colleague on Jan. 29, 2022.

Lead prosecutor Hank Brennan and Norfolk County Assistant District Attorney am Lally called a series of forensic specialists to bolster that theory.

The defense, which has rejected those allegations, focused much of its attention on a single expert who examined a key piece of evidence — vehicle data — and subjected that expert to hours of interrogation-like questioning as attorney Robert Alessi sought to dismantle the analyst’s contributions to the prosecution’s case.

“I’m trying to understand your statement,” an exasperated-sounding Alessi said at one point during cross-examination. “Isn’t it either you have a bachelor of science degree or you don’t?”

Read, who is charged with second-degree murder, motor vehicle manslaughter while driving under the influence and leaving the scene of a collision causing death, has remained chatty with reporters throughout the proceedings and said after court Wednesday that she feels “great” about the case so far.

She has maintained her innocence throughout her legal battle.

Her first trial ended with a hung jury last summer. Her defense team has said that she was framed by former and current law enforcement officers and others who were at the home where O’Keefe was found unresponsive early Jan. 29.

The defense has also said that the state trooper who led the investigation into O’Keefe’s death was biased and manipulated evidence. The trooper, who acknowledged sending unprofessional messages about Read but testified that his conduct did not affect the integrity of the investigation, was fired after an internal investigation found he violated agency rules.

In court earlier this week, experts offered a flurry of technical, sometimes highly complex details about the physical evidence linked to Read’s SUV: a strand of O’Keefe’s hair found on the Lexus’ rear quarter panel; bits of red plastic discovered on O’Keefe’s clothes that could have been from the SUV’s broken taillight.

The vehicle data examined by Shanon Burgess, a digital forensic analyst, is central to the prosecution’s case. Brennan has accused Read of reversing her Lexus into O’Keefe in a hit that left him dead, and Burgess’ analysis found that the SUV recorded a “backing event” outside the home where he was found unresponsive shortly after 6 a.m.

The defense spent hours grilling Burgess on everything from errors the expert acknowledged making in his analysis to the accuracy of his resume. At one point, the grueling back-and-forth prompted a startling admission from Burgess.

Even though his curriculum vitae and LinkedIn profile state that he has a bachelor’s degree in science from the University of Alabama, he has no more than an associate’s degree, Burgess testified. He began pursuing a bachelor’s in 2008, he said, but never completed the coursework.

When Alessi pressed Burgess to explain the misstatements, he attributed them to “errors” and “misinterpretations.”

“But you would agree those errors or misinterpretations have been in existence for some time?” the defense attorney responded.

“Yes,” Burgess said. “I’m being made aware of them now.”

At another point, Alessi pressed Burgess on what the defense lawyer described as a series of errors the expert made while analyzing three chips from Read’s SUV. In a document Burgess provided to the prosecution in October, Alessi said, the expert asserted that a previous analysis used in the case was incomplete because it did not capture all of the data from the chips.

In fact, Alessi said, it was Burgess who erred by making mistakes in his data conversion method. He confused megabits for megabytes, Alessi said, and gigabits for gigabytes. (Eight of the former equals one of the latter.)

“The entire foundation of your proposal was based on a fundamental misinterpretation of the difference between a computer bit and a computer byte, correct?” the defense lawyer said.

“No, not the entire thing,” Burgess responded.

“Well certainly a part of it was, correct?” Alessi said.

“Correct,” Burgess said.

“Since you wrote that, have you learned the difference between a bit and a byte?” the lawyer asked.

“I’ve always known the difference between a bit and a byte,” Burgess said.

Later, Alessi questioned Burgess about what he described as discrepancies between two reports he wrote in the case. The first, submitted in January of this year, sought to reconstruct the events of Jan. 29, 2022, using vehicle data. The second, submitted earlier this month — after Read’s retrial had already begun — was a supplemental report that sought to “clarify” parts of the initial document, Burgess said.

On the stand, Alessi asked him to explain one of those discrepancies in the supplemental report. On direct examination, Alessi said, Burgess told the prosecutor that he’d submitted the document on his own initiative in an effort to respond to a “misleading” claim that he later said came from a defense expert.

But the report itself stated the opposite, Alessi pointed out. In the document’s first line, which Alessi read in court, Burgess said he was submitting the additional analysis at the prosecutor’s request.

“Which is it?” Alessi asked.

“This is a holdover, so a copy and paste from my original report,” Burgess responded.

“Do you cut and paste important information from one report to the other without checking it for accuracy?” Alessi asked.

“I copy and paste certain portions,” Burgess said.

“You didn’t review it this time, though, did you?” Alessi said.

“No,” Burgess responded. “I didn’t think it was significant.”