NEW YORK, USA (AP) - A police sergeant from Trinidad, who was indicted on charges that he became a naturalised US citizen through a sham marriage, is also under investigation in the 2001 killing of an ex-girlfriend, authorities said Wednesday.

Federal and local law enforcement officials identified Sgt Martin Peters as a key suspect in the brutal slaying of Juliette Alexander, an immigration officer, in 2001.

Investigators hope Peters' arrest on federal charges will help crack the unsolved case, said Marc Raimondi, spokesman for US Immigration and Customs Enforcement.

"We want to see the murder solved and justice done," Raimondi said.

Peters, 41, was arraigned on Wednesday in federal court in Manhattan on immigration fraud and other charges and released on $20,000 bail.

Last year, Peters sued Police Commissioner Raymond Kelly and the city, alleging he was wrongly placed on desk duty and denied a promotion following Alexander's slaying. Calls to both his criminal and civil attorneys were not immediately returned.

The body of Alexander, 29, a newly-hired detention officer with the Immigration and Naturalization Service, was found in the foyer of her apartment building on January 16, 2001. She had been shot several times in the back of the head.

A second victim described as a friend of Peters, Nigel Callender, was found inside the apartment with gunshot wounds.

Callender - who baffled investigators by initially identifying Peters as the shooter, then recanting - also was arrested this week on immigration fraud charges.

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