Sessions, who opposes legal marijuana, left following through on prosecutions up to US attorneys like Lelling, who reiterated on Wednesday that he cannot guarantee immunity from federal prosecution for anyone involved in a marijuana business.

“I can’t do that,” Lelling said. “I’m not allowed to do that. So I won’t do that.”

But Lelling noted his office has 14 prosecutors who specialize in drug enforcement, and all 14 are spending most of their time chasing down bulk trafficking of heroin and other opioids.

Historically, the marijuana cases that they’ve pursued have been about bulk importation from Canada and Mexico, accompanied with money laundering, according to Lelling, who described that as a “traditional” case that rises to the level of a federal prosecution.

“Beyond that all I can say is we view this case by case,” he said.

Asked whether marijuana entrepreneurs looking at the Massachusetts market should relax, Lelling said, “I would not dare to say anything directly to the people entering the industry. Because again, something I’m sensitive to, I know that if you want to go into this industry, and you’re not in law enforcement or a lawyer, this may seem unsatisfying but I’m not a policy maker. I deal with the law as it is.”