Nicholas Roberts

“So our values that were calculated for the low was a 0.078 gram percent. The high was a 0.083 gram percent with the average being a 0.081.”

States the serum-conversion results Roberts calculated from the hospital result.

“And it's just so that it can encompass essentially anybody within the general population that they would be somewhere in between that lower limit and that upper limit.”

Explains why Roberts presented a broad retrograde-extrapolation range rather than one value.

Roberts described his forensic-science education, State Police Crime Lab toxicology work, proficiency testing, and the laboratory's accreditation requirements.

Roberts identified his serum-conversion report and testified that the reviewed medical record reported a serum alcohol level of 93 milligrams per deciliter from a specimen collected at 9:08 a.m.

“Yeah. You do have to base it on good -- your starting blocks have to be good. So you have to know the times in which the blood was drawn, the time of the incident and essentially what your value was for your BAC.”

Roberts identified the inputs he said were necessary for a reliable extrapolation.

“Yeah. There's a large range, like I said, due to the factors involved in the calculation. That's how it gets so large.”

Roberts attributed the breadth of his estimate to the factors in the calculation.

“It would have definitely caused a different time frame, depending on how long after the incident or the reported last drink, if there was another drink in between there.”

Roberts explained that the timing of any later drink could alter the retrograde-extrapolation time frame.