Officials say six men sold 74 weapons to undercover detectives in the New York City area where an officer was fatally shot last week.
Mayor de Blasio told reporters Tuesday their arrests come against the painful backdrop of NYPD officer Randolph Holder's death.
Holder was fatally shot in East Harlem on Oct. 20. The five-year veteran's funeral is Wednesday.
Thirty-year-old Tyrone Howard has been charged with robbery and murder. His lawyer has said there are many missing details in the case.
A state Supreme Court judge had referred Howard to a diversion program instead of prison last October in a drug case. He had skipped court and was wanted when Holder was shot.
The men arrested in the gun sting are to appear before the same judge Tuesday.