Commonwealth v. Read — Trial ArchiveNicholas Roberts
Testimony Impact
Nicholas Roberts, a forensic toxicologist with the Massachusetts Toxicology Lab, testified exclusively in Trial 1 on Day 18. His role was to convert Karen Read's hospital serum alcohol level—drawn at 9:08 a.m. on January 29, 2022—into a whole blood BAC and then extrapolate backward to estimate her BAC at 12:45 a.m., the time prosecutors identified as her last drink. His calculations placed Read's BAC at that earlier time somewhere between 0.135 and 0.292 g percent, a range the prosecution offered as evidence that Read was significantly impaired when she dropped off John O'Keefe.
Notable Quotes From The Record
“The level was at 93 milligrams per deciliter.”
The hospital serum alcohol reading that forms the basis for all subsequent BAC calculations.
“So the values that were calculated — the low was at 0.078 g percent, the high was 0.083 g percent, with the average being 0.081.”
The serum-to-whole-blood conversion result, showing Read's BAC at the time of hospital blood draw (9:08 a.m.) was near the legal limit.
“So the minimum amount that was calculated would have been 0.135 g percent.”
The low end of the retrograde extrapolation — even the minimum estimate places Read at nearly twice the legal limit at 12:45 a.m.
“The result was 0.292 g percent.”
The high end of the retrograde extrapolation, suggesting Read's BAC could have been nearly four times the legal limit.
“It would be difficult, yes.”
Concedes that precise serum-to-blood conversion is nearly impossible to predict for an individual person.
“Yeah, almost a sort of 120% swing.”
The prosecution's own expert concedes the enormous imprecision in his BAC calculation range.
“Uh, yeah.”
Roberts's concession on the final question — any post-12:45 a.m. drinking destroys his analysis — is the culmination of the cross.
“It was given to me that it was at 12:45. And as far as the BAC — or the serum conversion — that was coming from a medical record. So that was known as well, at 9:08 in the morning, the time that the blood was drawn.”
Reframes the inputs as known values from records rather than assumptions, countering the defense's characterization on cross.
“No.”
Roberts's final answer — that a last drink at 1:00 a.m. rather than 12:45 a.m. would not significantly impact his calculations — is the core rehabilitation point of the redirect.
Key Moments
- Roberts testified that Karen Read's hospital serum ethanol level of 93 mg/dL, after conversion to whole blood, yielded a BAC of approximately 0.081 g percent at the time of the 9:08 a.m. blood draw — a figure near the legal limit hours after the incident.
- Using retrograde extrapolation and assuming 12:45 a.m. as Read's last drink, Roberts calculated that her BAC at that time was between 0.135 and 0.292 g percent — a range the prosecution used to argue she was heavily intoxicated when she dropped O'Keefe off.
- On cross-examination, Roberts acknowledged that the range represented 'almost a sort of 120% swing,' a concession that became a focal point of the defense's challenge to the reliability of the entire analysis.
- Defense attorney Little closed her cross by establishing a clear invalidating condition: if Read had consumed any alcohol after 12:45 a.m. and before the 9:08 a.m. blood draw, Roberts agreed his entire calculation would be invalid — and he confirmed that assumption came from a police report, not from Read herself.
- On redirect, the prosecution rehabilitated Roberts by eliciting that a minor shift in the assumed last-drink time — from 12:45 a.m. to 1:00 a.m. — would not significantly change his extrapolation results, limiting the damage from the recross concession.