Christopher Halla, 42, is charged with manslaughter and tampering with evidence in the death of a 57-year-old South Hadley woman in May, the Northwestern District Attorney's Office said.
Investigators allege the woman tried to buy oxycodone from Halla, but he gave her a pill laced with metonitazene, a synthetic opioid far more potent than fentanyl. Fentanyl is the leading cause of the opioid overdose epidemic across the country.
State Police bought metonitazene from Halla in an undercover sting after the woman's death, the prosecutor said. He was previously charged with possession with intent to distribute Class-A drug, the prosecutor added.
The woman's name was not released.
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