CONCORD, N.H. — A substance made when the body breaks down heroin was present in a truck driver’s blood just hours after he was involved in a 2019 crash that killed seven motorcyclists, a forensic toxicologist testified Monday.

The metabolite, referred to as “6-MAM,” is unique to heroin and was found in the driver’s blood below “below the reporting limit,” the concentration of substances that can be measured accurately, said Donna Papsun of Pennsylvania-based NMS Labs. She had been asked to do additional testing by the New Hampshire State Police Forensic Laboratory.

Papsun’s testimony in the trial of Volodymyr Zhukovskyy expanded on what the National Transportation Safety Board says the driver told police about his drug use on the day of the crash.

Zhukovskyy’s lawyer, Steve Mirkin, has said his client did take heroin, fentanyl and cocaine on June 21, 2019, but said there’s no evidence he was impaired at the time of the crash and that police did not make any observations in the hours afterward suggesting that he was impaired.

Papsun was questioned in superior court in Lancaster, New Hampshire, by lawyers from both sides about how long heroin stays in the system, as well as other drugs that showed up in Zhukovskyy’s bloodwork, such as fentanyl, morphine and a metabolite found after cocaine consumption, and how those drugs could affect a person.

Prosecutors said Zhukovskyy, 26, of West Springfield, Massachusetts, was impaired and “weaved back and forth repeatedly” before the head-on crash on U.S. Route 2 in Randolph.

Zhukovskyý’s lawyers have said the lead motorcyclist, who died, was drunk and caused the crash. His blood-alcohol level registered at nearly twice the legal limit of .08 in New Hampshire.

Papsun testified that “6-MAM” breaks down fast and has a half-life — the time it takes in the body to reduce it by half — ranging from about five to six minutes to about 25 to 30 minutes.

She said it could take up to 3 1/2 hours for the body to clear its initial dose, but it could take less time than that for some people, “depending on an individual’s ability to break that down.”

Zhukovskyy’s first blood sample was taken shortly after 8:30 p.m., about two hours after the collision. She said the second blood sample, taken about an hour later, did not show a reliable reading of “6-MAM.”

Defense attorney Jay Duguay asked Papsun if just the presence of the substances alone in a person’s blood means that they are impaired.

“You can’t make that determination based on the toxicology alone?” he said.

“No,” she answered.

The motorcyclists who died were part of Jarheads Motorcycle Club, for Marines and their spouses. They were from New Hampshire, Massachusetts and Rhode Island and ranged in age from 42 to 62. They were part of a larger group that had just left a motel along the highway and were headed to an American Legion Post in Gorham for a fundraiser.

They were traveling east when the collision with the westbound truck occurred.