BRENTWOOD — A convicted police impersonator who allegedly used a stolen credit card to buy a vehicle that helped him pose as a U.S. Marshal lost his bid to keep jurors from hearing about his criminal past.

Eric Williams, 30, is headed to trial next week in Rockingham County Superior Court for duping a Derry car dealer on Dec. 23, 2010.

He faces charges of fraudulent use of a credit card and conspiracy to commit credit card fraud.

Prosecutors won permission by Judge Marguerite Wageling on Monday to question Williams about his past convictions if he decides to testify in his own defense.

Defense lawyer Neil Reardon argued that his client’s right to due process would be in jeopardy if the jury learned about the convictions.

Williams is already serving a 30-month federal prison sentence stemming from his latest stint posing as a U.S. Marshal in Massachusetts and stealing money from a Massachusetts woman he met online.

Before that theft, Williams bought a Ford Explorer from the Derry car dealer using a credit card belonging to his former landlord.

He tricked the dealership into thinking he had permission to use the card by having a woman — posing as his mother — tell a salesperson she owned the credit card, according to indictments.

The credit card was also used to buy other supplies, including dashboard lights to outfit the truck like a law enforcement vehicle, according to an affidavit.

Williams had stolen and cashed two checks from two Massachusetts women — one for $600, another for $700 — while posing as a deputy with the U.S. Marshal Service between last Jan. 11 and Jan. 15.

He pleaded guilty on Dec. 2 in U.S. District Court in Boston to seven counts of false impersonation of a federal officer and one count of theft of mail.

Williams victim’s included a woman he met online and dated for a brief time, and a roommate of another woman he dated briefly, according to court documents.

Prosecutors argued that jurors should hear about Williams past to judge his veracity if he decides to testify.

He has 15 convictions related to theft, forgery and receiving stolen property dating back to 2002, according to prosecutors.

In 2006, Williams was convicted in Rockingham County of theft and forgery charges for using a check stolen from his mother to buy a 1998 Crown Victoria from a Salem car dealer. Prosecutors say he used the vehicle while posing as a Norfolk County (Mass.) deputy sheriff.

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James A. Kimble may be reached at JKimble@newstote.com.