The phrase "a known associate of" is correct and usable in written English.
It can be used when referring to someone who is recognized as being connected or affiliated with another person, often in contexts involving relationships or networks.
Example: "The police are investigating a known associate of the suspect in the ongoing case."
Alternatives: "a recognized partner of" or "an identified affiliate of".
One of Cianci's co-defendants, Eddie Voccola, was a known associate of mobsters.
During a heavily armed assault at the hotel, gunmen loyal to Hutch shot dead 33-year-old David Byrne, a known associate of Kinahan.
After a few months, Archer applied for Home Office clearance to become an approved visitor, which involved being designated a "known associate of terrorists".
Tuesdays: The Brooklyn-based violinist and composer Jenny Scheinman, a known associate of Norah Jones, Bill Frisell, Madeleine Peyroux, and John Zorn, holds court.
We evaluated the northern flying squirrel (Glaucomys sabrinus griseifrons), a known associate of key habitat features and processes of old-growth forest, for its capacity as a broad-scale ecological indicator of temperate rainforest ecosystem condition in southeastern Alaska, USA.
One is a right-wing radical, a known associate of racist hate groups who made his living inspecting septic tanks, who was once convicted of illegally obtaining bubonic plague bacteria and later boasted about how easy it would be to kill hundreds of thousands of people by releasing it into the New York City subway, the authorities charge.
A few days after the bombing, the Yemenis brought in two known associates of bin Laden's for questioning.
Among the particulars in this nonjudicial form of indictment: "Known associates" of Mr. bin Laden named Sept. 11 as a date for action.
The document says that known associates of Mr. bin Laden named "the date for action as on or around 11 September".
*Immediately prior to 11 September, some known associates of bin Laden were naming the date for action as on or around 11 September.
The document says that known associates of Mr. bin Laden named "the date for action as on or around 11 September". Others were warned to return to Afghanistan before their plot unfolded, the document says.
