The girlfriend of one of the bandits who swiped $4 million in jewelry from a Midtown store last month was arrested in Connecticut — with one of the stolen diamonds in her purse, according to a report.

Stamford’s Narcotics and Organized Crime squad, along with officers from the NYPD, nabbed Shalonda Washington at her apartment at 6 a.m. on Sept. 10, Stamford police Capt. Richard Conklin told the Stamford Advocate.

Washington, 37, is believed to be the girlfriend of 39-year-old heist suspect Jaysean Sutton, who police are searching for in connection to last month’s Diamond District holdup, Conklin told the paper.

Sutton and two other accomplices posed as customers at popular jewelry spot Avianne & Co. on West 47th Street, then pulled guns on workers and forced them to open the store’s safe. The trio bagged an estimated $4 million in bling and ran off, police said.

When officers raided Washington’s apartment, she was gone — but had left three children alone in the home, the Advocate reported.

She was later arrested on charges of risking injury to a child, and while police were searching her, they found one of the pilfered jewels in her purse, Conklin told the paper.

The owner of the Manhattan store ID’ed the diamond as part of the stolen loot, saying it was worth $7,500, the paper reported.

A federal search uncovered several other pieces of jewelry that appear to be stolen from the Diamond District stole as well, Conklin said.

Washington was hit with an additional larceny charge and later released on a $7,500 bond, the paper reported.

Cops busted one of the heist’s suspects, Bronx resident Pedro Davila, on Sunday night in Florida.

Sutton — who has six prior arrests — is still on the loose, along with a third, unnamed suspect, officials said.