Prosecutors dropped a felony bomb scare charge against a coastside man who had already pleaded no contest after determining his was not the voice threatening to blow up Caltrain.

Antonio Derivera Santiago III, 26, of Pacifica, was first allowed to withdraw his no contest plea yesterday and then prosecutor Melissa McKowan asked that the case be dropped outright.

Prosecutors have believed for more than a year that Santiago called Caltrain out of boredom, telling a customer service representative that there was a bomb on train 101 and prompting an evacuation and full-scale search.

However, further investigation of the phone records done this summer showed that neither the phone used nor the voice belonged to Santiago, said Chief Deputy District Attorney Steve Wagstaffe.

Despite the discrepancy, Santiago had confessed and, only weeks after the Aug. 16 incident, pleaded no contest in return for no more than six months in jail.

Since December, he has asked to change his plea back to not guilty and face trial — and the possibility of three years in prison — but a hearing to determine if he could had been put off several times. In January, Judge Susan Etezadi denied the request based on insufficient reason because the original defense attorney was barred from testifying by the attorney-client privilege. Etezadi allowed a new motion to be filed and on Wednesday McKowan conceded the issue.

Wagstaffe said it is every prosecutor’s worst nightmare to convict an innocent man and he is glad Santiago has been out of custody on his own recognizance. Even so, Santiago has served approximately two months in custody on the charge, Wagstaffe said.

After Santiago first requested a plea change, defense attorney Jeff Hayden said prosecutors needed to look at the evidence rather than the confession. Hayden also described his client as having a low IQ, no high school degree and willing to agree to the story presented by law enforcement when confronted.

Hayden could not be reached for comment on the dismissal.

Michelle Durand can be reached by e-mail: michelle@smdailyjournal.com or by phone: (650) 344-5200 ext. 102.