CONCORD - A California man was sentenced to 20 years in federal prison for his role in the robbery of two jewelry stores and a credit union last year in Manchester and Tilton.

Walter Williams, 44, of Compton, was sentenced Tuesday in U.S. District Court for robbing Hannoush Jewelers and Northeast Credit Union, both in Manchester, and Kay Jewelers at the Tanger Outlets in Tilton.

The Manchester jewelry store was robbed Oct. 17, 2011, while Kay Jewelers was hit about two weeks later on Nov. 4, 2011. The credit unit was robbed on Dec. 19, 2011.

Williams and his then-girlfriend, Shyloe Johnson, were arrested in December 2011 at the Landmark Hotel in Laconia. Johnson pleaded guilty to aiding and abetting two of the robberies and was sentenced earlier this year.

Katie Falls, 29, was arrested and pleaded guilty for her part as the getaway driver in the Kay Jewelers robbery.

Delano Nelson, 49, of Compton, will be tried in January in the robberies.

Police said the California men came to New Hampshire specifically to commit armed robberies.

The Kay Jewelers robbery was particularly violent. Three store employees and four customers, including a mother and her young daughter, were inside the store when the "Scream"-masked robbers entered, ordered everyone to the floor at gunpoint and then began smashing jewelry cases with hammers.

The thieves netted between $250,000 to $280,000 in high-end gold jewelry in the two-minute heist. They took off in a black Land Rover, which they abandoned and then got into a second getaway car.

A break in the case came when a highway worker found two "Scream" masks off Exit 18 on Interstate 93. DNA results of hair and saliva on the masks led police to the suspects.

Williams and Nelson both have long felony records for armed robberies in California, according to police.