PORTLAND — A New Hampshire couple on Wednesday admitted to committing a string of robberies at banks and a credit union in Maine and New Hampshire last year, including a heist at a Lewiston credit union in September.

Crystal Dufault, 33, and Joseph Richards, 46, both of Manchester, pleaded guilty in U.S. District Court to armed bank robbery and conspiracy to commit armed bank robbery.

The charges stem from a slew of robberies in August and September, prosecutors said. Some of the robberies were committed by both of them; some by Richards alone. A total of $37,937 was stolen.

According to court records, the robberies were:

• Aug. 3, 2015, Norway Savings Bank in Freeport, committed by Richards;

• Aug. 14, 2015, Franklin Savings Bank in Franklin, N.H., by Dufault and Richards; 

• Sept. 4, 2015, University Credit Union in Portland, by Dufault and Richards; and

• Sept. 12, 2015, TD Bank in Lewiston, by Richards.

The Lewiston robbery was committed early on a Saturday morning, just after TD Bank had opened for business. Witnesses told police the robber fled into a waiting car parked across the street.

Richards was arrested later that day in Saco. Dufault was arrested a month later at her home, according to court records.

Investigators said a pellet gun was brandished during each of the robberies and the suspects absconded with $5,854 from Norway Savings Bank, $9,887 from Franklin Savings Bank, $12,308 from University Credit Union, and $9,888 from TD Bank in Lewiston.

The defendants face up to 25 years in prison and a $250,000 fine on each charge. They will be sentenced after completion of a presentence investigation report prepared by the U.S. Probation Office.

The joint investigation was conducted by the Franklin and Manchester (N.H.) police departments; the Freeport, Portland, Lewiston, Old Orchard Beach and Saco police departments; the Maine State Police; and the Southern Maine Gang Task Force.

The Task Force is comprised of agents and officers from the Federal Bureau of Investigation; the Bureau of Alcohol, Tobacco, Firearms and Explosives; the U.S. Drug Enforcement Administration; U.S. Immigration and Customs Enforcement’s Homeland Security Investigations; and the Portland, South Portland, Lewiston and Biddeford police departments.