NEW HAVEN Conn. (AP) – The U.S. Drug Enforcement Agency was analyzing a Connecticut heroin sample Monday as investigators worked to determine whether four apparent overdoses were linked to an unusually pure batch of heroin or one spiked with poison.

“We don’t know what we have, but there’s something going on,” said Capt. Phil Kennedy of New Britain, where three people have died of apparent heroin overdoses in the last few weeks.

A fourth fatal overdose in Meriden was reported on Feb. 11, according to the University of Connecticut Health Center. When officers in New Britain reviewed their call log, they found as many as six other drug-related medical reports.

Kennedy said Monday that the he was waiting for word from the DEA laboratory, where he said investigators are making the analysis a priority. Heroin overdoses are not unusual, but such clusters usually indicate either an abnormally pure drug or one containing a poison.

Dealers normally dilute, or “cut,” heroin with things like powdered milk or sugar to increase its volume. Occasionally, investigators discover batches of heroin cut with rat poison or powdered soap.

In its second public health update in four days, the University of Connecticut Health Center warned public health agencies Monday to look for potentially “tainted” heroin. Police departments, homeless shelters and drug rehab centers were all alerted.

But police aren’t rushing to judgment.

A cluster of heroin deaths can as easily be caused by spikes in purity as it can by toxic cutting agents.

In Connecticut, street heroin is usually about 5 to 15 percent pure, said Sgt. Blake J. Stine, a member of the State Police Narcotics Task Force. Nationally, the average is 38 percent, according to the DEA.

Stine said there’s no evidence that heroin purity is up statewide. A sudden increase in purity in one area is often a sign of a new dealer, a competitive market or a strong supply.

“Every couple years, a stronger cut of heroin surfaces and we some overdoses and deaths,” Stine said. “Normally that’s what it is.”