REDWOOD CITY, Calif. (AP) - A judge ruled that evidence police gathered using electronic devices to track Scott Peterson after his pregnant wife disappeared can be used in his murder trial, despite defense objections that the technology is unreliable.

Because global positioning system technology has yet to be tested in state criminal court, prosecutors had to establish its reliability and demonstrate the technology was used correctly.

Judge Alfred A. Delucchi decided Tuesday they had met those legal tests.

Peterson's lawyer, Mark Geragos, tried to convince the judge that temporary glitches rendered unreliable the devices that Modesto police secretly attached to vehicles Peterson drove before his April 2003 arrest.

Hugh Roddis, president of the company that sold Modesto police the three devices, said that covertly placed global positioning devices are a "good investigative tool."

The satellite-based radio navigation system can pinpoint locations within feet and is in common use, including in commercial aircraft.

Geragos seized on tracking errors in several of the devices Modesto police used, including one that he said didn't work for nearly three weeks.

Roddis blamed the errors on inaccurate maps, a faulty wireless antenna and a bad microprocessor connection.

During testimony last week, prosecutors said police used the devices to trail Peterson to San Francisco Bay at least once in January 2003. Police installed the devices in vehicles Peterson owned, borrowed and rented after Laci Peterson disappeared on Christmas Eve 2002. Scott Peterson said he was fishing on the Bay at the time.

If convicted of the murders of his wife and their unborn son, Peterson could face the death penalty.

The judge also tossed out an interview with a woman prosecutors believe may have mistaken for Laci Peterson by witnesses.

At least three neighbors said they saw Laci Peterson walking her dog on Christmas Eve morning - after prosecutors claim Scott Peterson killed her. Prosecutors have suggested the neighbors saw Kristin Dempewolf, who, like Laci Peterson, had shoulder-length brown hair and was pregnant.

Delucchi said he wouldn't allow the interview because authorities didn't follow proper procedures.