Stamford police say they raided a drug lab and made the largest seizure of the deadly opioid carfentanil in the city's history.

The synthetic drug is 100 times stronger than fentanyl, which is deadly on its own, and 5,000 times more potent than heroin, police say.

According to investigators, officers executed a search warrant at 77 West Hill Circle and found a functioning pill lab set up to make counterfeit Percocet pills with three presses, cutting agents and pill dyes. They also found an assault rifle.

"Very ominous when you go into a location and you see they have their own hazmat suits and respirators there," one official told News 12. "That certainly gives you pause."

Police arrested David Reichard, a 29-year-old who lives at the address, on drug possession charges, but authorities say more charges are likely. Additional arrests are also likely.

Local police called in the federal Drug Enforcement Administration, and agents spent several hours processing the scene.

Stamford Police Capt. Richard Conklin says the DEA team told him it was the largest such operation it had seen in New England.

Reichard is being held on $750,000 bond. His attorney says he was a house guest for the past few months and may have been caught in the "wrong place, wrong time."

One neighbor, who asked not to go on camera, told News 12 that she often saw people in their 20s coming and going from the house, but she says she did not suspect anything until police showed up.