At first, the cluster of deadly overdoses reviewed by the Hennepin County medical examiner’s office this winter gave no indication that a new opioid hitting the streets was instantly killing its users.

The victims each showed telltale signs of drug abuse, but their autopsy tests came back negative for the most commonly abused substances.

Nearly two months after the first reported overdose in late January, medical investigators were stunned to learn that the drug carfentanil — used to tranquilize elephants — could be responsible for at least nine other deaths. The Drug Enforcement Administration went public with the discovery 30 hours after it learned of the results.

Carfentanil, a white powder that looks similar to other opioids, can’t be diluted enough to make it safe for humans, said Ken Solek, the DEA’s assistant special agent in charge in Minnesota. Little medical research exists on the drug, but Solek described it as “fentanyl on steroids” — and 10,000 times more potent than morphine.

Ingesting just two salt-sized grains of carfentanil can mean instant death, ­officials warn.

State and federal law enforcement agents are bracing for more carfentanil overdoses by cobbling together a multipronged response and prevention plan. The strategy includes intense education efforts, stronger synthetic drug legislation and ongoing diplomatic talks with China, the main source for carfentanil.

“If dealers had any ethics and morals, they would stop lacing this substance with other drugs. But they don’t care about anybody,” said Apple Valley Police Chief Jon Rechtzigel, who had an overdose in his city.

A new scourge

The first verified overdose of carfentanil in the United States occurred last July in Akron, Ohio, where several dozen people died during a three-week period. The DEA made more than 400 seizures of carfentanil across eight states from July through October.

The drug has mainly traded on the East Coast. But carfentanil overdoses, in combination with other drugs, were confirmed in five Minnesota cases from Jan. 30 to Feb. 17. The dead, age 23 to 43, were from Minneapolis, Apple Valley and Faribault.

Erick Taft, 31, was the first victim. He had struggled with addiction since his late teens, but had been through treatment, graduated from technical college and had a steady girlfriend and a job in recent years. But the loss of his job, breakup with his girlfriend and death of his father appeared to push him to use drugs again, said his mother, Anne Taft-Wild. She said his heroin purchase contained nearly all carfentanil.

“When I was called to his house by his roommate, I was hoping he was just sick and I could visit him in the hospital,” Taft-Wild said. “But it looked like a crime scene. People have to know buying heroin now is just a crapshoot.”

Wisconsin recorded its first case last month, with the death of a homeless man in Milwaukee.

Police investigating the overdoses are making progress, officials say. But they declined to comment on the possible source of the carfentanil or whether the cases are connected.

“We all felt this drug could move our way,” said Faribault Police Chief Andy Bohlen, who heads the state’s Violent Crime Coordinating Council.

Police and medical investigators are still waiting for toxicology results on five more overdose cases. Although testing for carfentanil is improving, current methods take weeks to process due to the tiny amounts of the drug found in victims and the lack of labs equipped to assess it.

The investigations will be coordinated through a federally funded initiative started by Hennepin County Sheriff Rich Stanek last year to address growing heroin and fentanyl use in the metro area. Last year, 153 people died from opioid overdoses in the county.

“We may need to start looking at every overdose like a crime,” Stanek said. “But it’s so tough with carfentanil. People can order it off the dark web and have it delivered like pizza. How sad is that?”

(The dark web refers to internet sites that require special software to access and is often used for illicit purposes.)

The Minnesota Bureau of Criminal Apprehension has assigned agents throughout the state to help investigate carfentanil cases. The agency is seeking funding from the Legislature for a new criminal analyst to work on drug initiatives. BCA Superintendent Drew Evans said the agency already has exceeded the 75 fentanyl cases it handled last year, and he worries about the more deadly carfentanil.

‘Looking for a needle in a haystack’

Hennepin County Medical Examiner Andrew Baker said his staff expected routine findings for the 10 overdoses it examined this year. When the usual drugs didn’t appear, they tested for novel drug agents.

Solek said identifying carfentanil was a major achievement, but it left police scrambling for ways to stop the influx into Minnesota and looking for ways to keep drug dealers from using it. Carfentanil can also be dangerous for officers, police dogs, first responders and jail intake and emergency room personnel who come in contact with it. Agencies are training their employees about it, and they keep the opioid antidote naloxone on hand just in case.

“Every resource is being thrown at the problem, and we are definitely making progress,” Solek said. “It can feel like looking for a needle in a haystack. But I’m positive we will bring this problem to a successful conclusion.”

The biggest break in the battle against carfentanil came in March when China declared it and three similar drugs illegal, closing a major regulatory loophole. Even so, new chemical combinations of carfentanil and fentanyl are quickly being created to replace banned formulas, Solek said. He said legislation has been introduced in Congress to make it easier to prosecute the sale of synthetic substances that are substantially similar to illegal drugs.

Another important bill, sponsored by U.S. Sen. Amy Klobuchar, D-Minn., with bipartisan support, would require packages from foreign countries to declare what’s in them, who sent them and where they’re going. The law could help police find dealers like the one who sold Taft and the other victims tainted drugs.

Taft-Wild said she hasn’t received any updates from investigators in the three months since her son’s funeral filled a local church. She said he wanted to be a chemical dependency counselor, and she was sure he was clean less than two weeks before he died. She said she couldn’t persuade him to continue his recovery with inpatient treatment.

“I used to wake up worrying about him and go to bed worrying about him,” she said.