ANCHORAGE (AP) — For years, the man known as Rafael Espinoza was widely respected as an exemplary police officer popular among his peers here.

All that ended last week when the authorities accused him of actually being Rafael Mora-Lopez, a Mexican citizen who stole another man’s identity and was in the United States illegally.

“His reputation here is one of a hard-working officer, one who was very professional,” Chief Mark Mew of the Anchorage police said Friday in announcing Mr. Mora-Lopez’s arrest. “The problem, obviously, is he is not Rafael Espinoza.”

Mr. Mora-Lopez pleaded not guilty on Friday in Federal District Court in Anchorage to a charge of passport fraud, which carries a maximum 10-year sentence. At his arraignment, Mr. Mora-Lopez told a federal magistrate that he was 47, even though officials listed his age as 51.