There are still a few unknowns in the case of Rafael Mora-Lopez, reportedly a Mexican national who is accused of posing as an American citizen while working for the Anchorage Police Ddepartment.

But Police Chief Mark Mew said more answers will be forthcoming.   Mew says there's a simple explanation for why the department's fingerprint-based background check did not discover the existence of an American citizen named Rafael Espinoza, the name used by former anchorage officer Rafael Mora-Lopez.   The real Espinoza, who has dual citizenship, does not live in the United States and does not have fingerprints on file here.   "There was no record in the United States beyond the fact that he existed. So it was an empty slate, in other words," Mew said.   Espinoza's application for a U.S. passport is what triggered last week's arrest of Mora-Lopez, Mew said.   The file on the polygraph examination that Mora-Lopez was given before his hire was located this afternoon, Mew said, but it remains to be seen whether a flaw in the examination procedure allowed the fake name to escape detection.   "I don't want to assume anything right now,” he said. “I've never had reason to suspect we have a fundamental error in our system. But we'll look and see. We'll go wherever the data tells us to go.”    Mew said the case of Mora-Lopez has harmed department morale, particularly coming so soon after the conviction of former officer Anthony Rollins for sexual assaults.   "We're trying to recover from the negative coverage associated with the Rollins matter. We see these both as problems, as legitimate problems. We see them as different kinds of problems. We're not sure the public sees them as different kinds of problems."   There could be additional charges against Mora-Lopez in coming weeks.   Meanwhile, APD must cope with another hit to its reputation.   Mew said he had been given legal advice not to discuss whether Mora-Lopez and Espinoza knew each other, how long Mora-Lopez used the false identity or whether Mora-Lopez had been in Anchorage since his entry into the United States from Mexico in 1989.   Mew said Mora-Lopez was well-liked on the force and received an award for saving a life last year by administering CPR.