As Karen Read's retrial zeroed in on a possible murder weapon, an expert's credibility was challenged

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.

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 Adam 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?”