On that fateful day the Feds busted Tekashi 6ix9ine and 11 other Nine Treys they also took in NYPD cop Arlicia Robinson.

Robinson wasn't part of the RICO case against 6ix9ine and his Blood bros, nor was her arrest publicized at the time.

It came out during the trial of  Aljermiah "Nuke" Mack and Anthony "Harv" Ellison that Robinson helped the Tr3yways smuggle heroin on three occasions.

Nuke was ultimately convicted of distributing heroin, thanks in part to the testimony of 6ix9ine and Kristian "CEO Kris" Cruz, who'd been snitching to the Feds for years.  

Sergeant Robinson -- who worked for the Housing Bureau and oversaw 20 housing projects throughout Brooklyn -- has been charged with possession of heroin with intent to distribute 1 kilogram or more.

She was supposed to be in court this week, but her appearance got pushed back to November 25 so she can negotiate a plea deal.

"The additional time is necessary for the parties to complete their plea negotiations," Sgt. Robinson's lawyer Justine Harris told Judge Alvin K. Hellerstein.

Robinson is free on a 100K bond but suspended from the NYPD.