SAN JOSE -- An ex-teacher from San Jose who took off to Vietnam to avoid prosecution for child pornography charges was arrested Wednesday evening at San Francisco International Airport by federal authorities after local investigators learned he was returning to the country.

Nathan Forstell, 45, was turned over to the custody of the San Jose Police Department and was booked into the Santa Clara County Jail, where he is being held on $25,000 bail.

Forstell was arrested in March 2013 after an investigation by SJPD's sexual-assault unit and Internet Crimes Against Children task force alleged he had been viewing and sharing child pornography. Police said a search of his home yielded nearly 1,000 illicit images and videos, some depicting children between 4 and 9 years old performing sexual acts.

At the time of his arrest, Forstell was teaching physical education at an elementary school in Seaside in Monterey County; he was arrested at the school. Forstell also previously worked as a substitute teacher in the Alum Rock School from February 2008 until February 2013, after which he changed school districts.

There is no evidence to suggest he victimized any of the students under his supervision. Employer background checks did not turn up any allegations against him.

The day after he was arrested, Forstell apparently tried to commit suicide by overdosing on an undisclosed medication, prompting him to be placed on a 72-hour psychiatric hold.

While the timeline is unclear, at some point after his release on bail he fled to Vietnam, authorities said. Recently, SJPD sex-crimes detectives learned that Forstell was returning to the United States and notified federal Customs and Border Protection officials at SFO.

Additional details about Forstell's disappearance were not immediately available Thursday.

Contact Robert Salonga at 408-920-5002. Follow him at Twitter.com/robertsalonga.