The judge presiding over the trial of a man accused of killing three people while driving drunk expressed reservations Tuesday about the reliability of a key prosecution witness, but said he would allow the testimony Wednesday in the interest of fairness.

Oniel Sharpe Jr., 25, a maintenance worker from Springfield Gardens, is charged with aggravated vehicular homicide and other crimes in the July 12, 2015, deaths of Ancio Ostane, 37, and his children, Andy, 8, and Sephora, 4, all of St. Albans. He is accused of driving drunk at high speed into the back of the family’s Toyota RAV4 and then fleeing the scene after their vehicle exploded, leaving all three to burn to death, trapped in their car on the Southern State Parkway at Exit 41s in Bay Shore.

New York State Police didn’t find Sharpe until more than four hours after the crash and by then his blood alcohol content was 0.05 percent, a forensic toxicologist testified. Another forensic scientist is expected to testify Wednesday that a method called retrograde extrapolation would show his blood alcohol content was 0.12 percent at the time of the crash, above the legal threshold of 0.08 percent.

Defense attorney Jonathan Manley in his opening statement called retrograde extrapolation “junk science” and said it was about as scientifically valid as astrology.

Outside the jury’s presence, state Supreme Court Justice Fernando Camacho told attorneys in the case Tuesday that he is concerned about the accuracy of retrograde extrapolation, but explained why he would permit it in this case.

“It’s not an exact science,” Camacho said. “There are so many variables.”

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Those variables include what a defendant ate and when, height, weight, stress and other factors. Further complicating the issue in this case is that no one knows what or when Sharpe ate before his blood was tested. A big meal before or soon after he was drinking could delay his body’s absorption of alcohol, leading to an inaccurate estimate from retrograde extrapolation.

The judge said he concluded it would be unfair to prevent prosecutors from presenting the testimony in light of claims that Sharpe left the scene and avoided police until his level of intoxication had lessened.

Police asked Sharpe, who was generally cooperative after his arrest, what he’d eaten but he didn’t answer the question.

“That’s a big variable,” Camacho said.

Because a defendant’s right to remain silent can’t be used against him, Camacho said prosecutors can’t ask about Sharpe’s non-answer about what he’d eaten.

At the same time, however, Camacho said the principles behind retrograde extrapolation are sound. After a person ingests alcohol, its content in the bloodstream peaks and then gradually dissipates.

“The issue is permitting the [forensic] expert to give an actual blood alcohol content at the time of the incident,” Camacho said.